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Add Android default global usings in MSBuild targets #6075

Closed
Tracked by #6076
mhutch opened this issue Jul 7, 2021 · 2 comments · Fixed by #6118
Closed
Tracked by #6076

Add Android default global usings in MSBuild targets #6075

mhutch opened this issue Jul 7, 2021 · 2 comments · Fixed by #6118
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@jonathanpeppers
Labels
Area: App+Library Build Issues when building Library projects or Application projects.
Milestone
.NET 6

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@mhutch
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mhutch commented Jul 7, 2021

Following the pattern in dotnet/sdk#18459, the Android SDK targets should contain default global usings that can be disabled by an MSBuild property.
@mhutch mhutch added Area: App+Library Build Issues when building Library projects or Application projects. needs-triage Issues that need to be assigned. labels Jul 7, 2021
@mhutch mhutch added this to the .NET 6 milestone Jul 7, 2021
@mhutch mhutch mentioned this issue Jul 7, 2021
Closed
@jpobst jpobst assigned jonathanpeppers and unassigned jpobst Jul 7, 2021
@jpobst jpobst removed the needs-triage Issues that need to be assigned. label Jul 7, 2021
@mhutch mhutch mentioned this issue Jul 7, 2021
Closed
2 tasks
@jonathanpeppers jonathanpeppers mentioned this issue Jul 7, 2021
Closed
jonathanpeppers added a commit to jonathanpeppers/xamarin-android that referenced this issue Jul 23, 2021
@jonathanpeppers
[One .NET] support latest C #10 language features
e628acd 
Fixes: dotnet#6075
Fixes: dotnet#6076
Context: xamarin/xamarin-macios#12173

We need to make two sets of changes for C# 10:

1. Support "global usings". Our .NET 6 templates should have no
   `using` statements at the top of `.cs` files.
2. Use `$(Nullable)` `enable` by default in project templates.

To test this, our .NET 6 MSBuild tests use `Nullable=enable` by
default and do no include `using` statements.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests. The
"legacy" Xamarin.Android tests will use the original file.
@jonathanpeppers jonathanpeppers mentioned this issue Jul 23, 2021
Merged
jonathanpeppers added a commit to jonathanpeppers/xamarin-android that referenced this issue Jul 23, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features
245ec40 
Fixes: dotnet#6075
Fixes: dotnet#6076
Context: xamarin/xamarin-macios#12173

We need to make two sets of changes for C# 10:

1. Support "global usings". Our .NET 6 templates should have no
   `using` statements at the top of `.cs` files.
2. Use `$(Nullable)` `enable` by default in project templates.

To test this, our .NET 6 MSBuild tests use `Nullable=enable` by
default and do no include `using` statements.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests. The
"legacy" Xamarin.Android tests will use the original file.
@jonpryor
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As per #6118 (comment), I'm starting to wonder if anything should be added to @(Import) for Android apps. It feels like anything we add would be likely to introduce type resolution conflicts for MAUI and BCL types.

jonathanpeppers added a commit to jonathanpeppers/xamarin-android that referenced this issue Jul 26, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features
f7a5e1d 
Fixes: dotnet#6075
Fixes: dotnet#6076
Context: xamarin/xamarin-macios#12173

We need to make two sets of changes for C# 10:

1. Support "global usings". Our .NET 6 templates should have no
   `using` statements at the top of `.cs` files.
2. Use `$(Nullable)` `enable` by default in project templates.

To test this, our .NET 6 MSBuild tests use `Nullable=enable` by
default and do no include `using` statements.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests. The
"legacy" Xamarin.Android tests will use the original file.
jonathanpeppers added a commit to jonathanpeppers/xamarin-android that referenced this issue Aug 4, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features
fdd34a1 
Fixes: dotnet#6075
Fixes: dotnet#6076
Context: xamarin/xamarin-macios#12173

We need to make two sets of changes for C# 10:

1. Support "global usings". Our .NET 6 templates should have no
   `using` statements at the top of `.cs` files.
2. Use `$(Nullable)` `enable` by default in project templates.

To test this, our .NET 6 MSBuild tests use `Nullable=enable` by
default and do no include `using` statements.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests. The
"legacy" Xamarin.Android tests will use the original file.

Our default `global using` are:

   global using global::Android.App;
   global using global::Android.Widget;
   global using Bundle = global::Android.OS.Bundle;

The last one is intentionally not bringing in `Android.OS`, because
`Android.OS.Environment` would conflict with `System.Environment`.

I also had to write our own target to generate the using for `Bundle`,
because the dotnet/sdk always prepends `global::`:

https://github.com/dotnet/sdk/blob/86946f52cd012cefd811b25287a8da034bf082a3/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.GenerateImplicitNamespaceImports.targets#L46
jonathanpeppers added a commit to jonathanpeppers/xamarin-android that referenced this issue Aug 4, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features
8004dd1 
Fixes: dotnet#6075
Fixes: dotnet#6076
Context: xamarin/xamarin-macios#12173

We need to make two sets of changes for C# 10:

1. Support "global usings". Our .NET 6 templates should have no
   `using` statements at the top of `.cs` files.
2. Use `$(Nullable)` `enable` by default in project templates.

To test this, our .NET 6 MSBuild tests use `Nullable=enable` by
default and do no include `using` statements.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests. The
"legacy" Xamarin.Android tests will use the original file.

Our default `global using` are:

   global using global::Android.App;
   global using global::Android.Widget;
   global using Bundle = global::Android.OS.Bundle;

The last one is intentionally not bringing in `Android.OS`, because
`Android.OS.Environment` would conflict with `System.Environment`.

I also had to write our own target to generate the using for `Bundle`,
because the dotnet/sdk always prepends `global::`:

https://github.com/dotnet/sdk/blob/86946f52cd012cefd811b25287a8da034bf082a3/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.GenerateImplicitNamespaceImports.targets#L46
jonathanpeppers added a commit to jonathanpeppers/xamarin-android that referenced this issue Aug 4, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features
91c1ad9 
Fixes: dotnet#6075
Fixes: dotnet#6076
Context: xamarin/xamarin-macios#12173

We need to make two sets of changes for C# 10:

1. Support "global usings". Our .NET 6 templates should have no
   `using` statements at the top of `.cs` files.
2. Use `$(Nullable)` `enable` by default in project templates.

To test this, our .NET 6 MSBuild tests use `Nullable=enable` by
default and do no include `using` statements.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests. The
"legacy" Xamarin.Android tests will use the original file.

Our default `global using` are:

   global using global::Android.App;
   global using global::Android.Widget;
   global using Bundle = global::Android.OS.Bundle;

The last one is intentionally not bringing in `Android.OS`, because
`Android.OS.Environment` would conflict with `System.Environment`.

I also had to write our own target to generate the using for `Bundle`,
because the dotnet/sdk always prepends `global::`:

https://github.com/dotnet/sdk/blob/86946f52cd012cefd811b25287a8da034bf082a3/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.GenerateImplicitNamespaceImports.targets#L46
jonathanpeppers added a commit to jonathanpeppers/xamarin-android that referenced this issue Aug 5, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features
ce8f4b7 
Fixes: dotnet#6075
Fixes: dotnet#6076
Context: xamarin/xamarin-macios#12173

We need to make two sets of changes for C# 10:

1. Support "global usings". Our .NET 6 templates should have no
   `using` statements at the top of `.cs` files.
2. Use `$(Nullable)` `enable` by default in project templates.

To test this, our .NET 6 MSBuild tests use `Nullable=enable` by
default and do no include `using` statements.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests. The
"legacy" Xamarin.Android tests will use the original file.

Our default `global using` are:

   global using global::Android.App;
   global using global::Android.Widget;
   global using Bundle = global::Android.OS.Bundle;

The last one is intentionally not bringing in `Android.OS`, because
`Android.OS.Environment` would conflict with `System.Environment`.

I also had to write our own target to generate the using for `Bundle`,
because the dotnet/sdk always prepends `global::`:

https://github.com/dotnet/sdk/blob/86946f52cd012cefd811b25287a8da034bf082a3/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.GenerateImplicitNamespaceImports.targets#L46
@mhutch
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mhutch commented Aug 11, 2021

@jonpryor if there are type conflicts between system types and android types we can make aliasing choices and emit those too.

jonathanpeppers added a commit to jonathanpeppers/xamarin-android that referenced this issue Aug 17, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features
1064f4f 
Fixes: dotnet#6075
Fixes: dotnet#6076
Context: xamarin/xamarin-macios#12173

We need to make two sets of changes for C# 10:

1. Support "global usings". Our .NET 6 templates should have no
   `using` statements at the top of `.cs` files.
2. Use `$(Nullable)` `enable` by default in project templates.

To test this, our .NET 6 MSBuild tests use `Nullable=enable` and
`ImplicitUsings=enable` by default and do not include `using`
statements in `.cs` files.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests. The
"legacy" Xamarin.Android tests will use the original file.

Our default `global using` are:

    global using global::Android.App;
    global using global::Android.Widget;
    global using Bundle = global::Android.OS.Bundle;

The last one is intentionally not bringing in `Android.OS`, because
`Android.OS.Environment` would conflict with `System.Environment`.

So `AutoImport.props` should become:

    <ItemGroup Condition=" '$(TargetPlatformIdentifier)' == 'android' and ('$(ImplicitUsings)' == 'true' or '$(ImplicitUsings)' == 'enable') ">
      <Using Include="Android.App" />
      <Using Include="Android.Widget" />
      <Using Include="Android.OS.Bundle" Alias="Bundle" />
    </ItemGroup>

So these items are present at the time `.csproj` files are evaluated.

Any templates will add:

    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>

If users want to configure these settings, they can remove
`$(ImplicitUsings)` from the `.csproj` completely or remove specific
`@(Using)` items:

    <ItemGroup>
      <Using Remove="Android.App" />
    </ItemGroup>
jonathanpeppers added a commit to jonathanpeppers/xamarin-android that referenced this issue Aug 17, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features
2443637 
Context: dotnet/sdk#19521
Fixes: dotnet#6075
Fixes: dotnet#6076

We need to make two sets of changes for C# 10:

1. Support "global usings". Our .NET 6 templates should have no
   `using` statements at the top of `.cs` files.
2. Use `$(Nullable)` `enable` by default in project templates.

To test this, our .NET 6 MSBuild tests use `Nullable=enable` and
`ImplicitUsings=enable` by default and do not include `using`
statements in `.cs` files.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests. The
"legacy" Xamarin.Android tests will use the original file.

Our default `global using` are:

    global using global::Android.App;
    global using global::Android.Widget;
    global using Bundle = global::Android.OS.Bundle;

The last one is intentionally not bringing in `Android.OS`, because
`Android.OS.Environment` would conflict with `System.Environment`.

So `AutoImport.props` should become:

    <ItemGroup Condition=" '$(TargetPlatformIdentifier)' == 'android' and ('$(ImplicitUsings)' == 'true' or '$(ImplicitUsings)' == 'enable') ">
      <Using Include="Android.App" />
      <Using Include="Android.Widget" />
      <Using Include="Android.OS.Bundle" Alias="Bundle" />
    </ItemGroup>

So these items are present at the time `.csproj` files are evaluated.

Any templates will add:

    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>

If users want to configure these settings, they can remove
`$(ImplicitUsings)` from the `.csproj` completely or remove specific
`@(Using)` items:

    <ItemGroup>
      <Using Remove="Android.App" />
    </ItemGroup>
jonathanpeppers added a commit to jonathanpeppers/xamarin-android that referenced this issue Aug 19, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features
30e90db 
Context: dotnet/sdk#19521
Fixes: dotnet#6075
Fixes: dotnet#6076

We need to make two sets of changes for C# 10:

1. Support "global usings". Our .NET 6 templates should have no
   `using` statements at the top of `.cs` files.
2. Use `$(Nullable)` `enable` by default in project templates.

To test this, our .NET 6 MSBuild tests use `Nullable=enable` and
`ImplicitUsings=enable` by default and do not include `using`
statements in `.cs` files.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests. The
"legacy" Xamarin.Android tests will use the original file.

Our default `global using` are:

    global using global::Android.App;
    global using global::Android.Widget;
    global using Bundle = global::Android.OS.Bundle;

The last one is intentionally not bringing in `Android.OS`, because
`Android.OS.Environment` would conflict with `System.Environment`.

So `AutoImport.props` should become:

    <ItemGroup Condition=" '$(TargetPlatformIdentifier)' == 'android' and ('$(ImplicitUsings)' == 'true' or '$(ImplicitUsings)' == 'enable') ">
      <Using Include="Android.App" />
      <Using Include="Android.Widget" />
      <Using Include="Android.OS.Bundle" Alias="Bundle" />
    </ItemGroup>

So these items are present at the time `.csproj` files are evaluated.

Any templates will add:

    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>

If users want to configure these settings, they can remove
`$(ImplicitUsings)` from the `.csproj` completely or remove specific
`@(Using)` items:

    <ItemGroup>
      <Using Remove="Android.App" />
    </ItemGroup>
jonathanpeppers added a commit to jonathanpeppers/xamarin-android that referenced this issue Aug 19, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features
43e480a 
Context: dotnet/sdk#19521
Fixes: dotnet#6075
Fixes: dotnet#6076

We need to make two sets of changes for C# 10:

1. Support "global usings". Our .NET 6 templates should have no
   `using` statements at the top of `.cs` files.
2. Use `$(Nullable)` `enable` by default in project templates.

To test this, our .NET 6 MSBuild tests use `Nullable=enable` and
`ImplicitUsings=enable` by default and do not include `using`
statements in `.cs` files.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests. The
"legacy" Xamarin.Android tests will use the original file.

Our default `global using` are:

    global using global::Android.App;
    global using global::Android.Widget;
    global using Bundle = global::Android.OS.Bundle;

The last one is intentionally not bringing in `Android.OS`, because
`Android.OS.Environment` would conflict with `System.Environment`.

So `AutoImport.props` should become:

    <ItemGroup Condition=" '$(TargetPlatformIdentifier)' == 'android' and ('$(ImplicitUsings)' == 'true' or '$(ImplicitUsings)' == 'enable') ">
      <Using Include="Android.App" />
      <Using Include="Android.Widget" />
      <Using Include="Android.OS.Bundle" Alias="Bundle" />
    </ItemGroup>

So these items are present at the time `.csproj` files are evaluated.

Any templates will add:

    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>

If users want to configure these settings, they can remove
`$(ImplicitUsings)` from the `.csproj` completely or remove specific
`@(Using)` items:

    <ItemGroup>
      <Using Remove="Android.App" />
    </ItemGroup>
jonathanpeppers added a commit to jonathanpeppers/xamarin-android that referenced this issue Aug 20, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features
9e96e08 
Context: dotnet/sdk#19521
Fixes: dotnet#6075
Fixes: dotnet#6076

We need to make two sets of changes for C# 10:

1. Support "global usings". Our .NET 6 templates should have no
   `using` statements at the top of `.cs` files.
2. Use `$(Nullable)` `enable` by default in project templates.

To test this, our .NET 6 MSBuild tests use `Nullable=enable` and
`ImplicitUsings=enable` by default and do not include `using`
statements in `.cs` files.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests. The
"legacy" Xamarin.Android tests will use the original file.

Our default `global using` are:

    global using global::Android.App;
    global using global::Android.Widget;
    global using Bundle = global::Android.OS.Bundle;

The last one is intentionally not bringing in `Android.OS`, because
`Android.OS.Environment` would conflict with `System.Environment`.

So `AutoImport.props` should become:

    <ItemGroup Condition=" '$(TargetPlatformIdentifier)' == 'android' and ('$(ImplicitUsings)' == 'true' or '$(ImplicitUsings)' == 'enable') ">
      <Using Include="Android.App" />
      <Using Include="Android.Widget" />
      <Using Include="Android.OS.Bundle" Alias="Bundle" />
    </ItemGroup>

So these items are present at the time `.csproj` files are evaluated.

Any templates will add:

    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>

If users want to configure these settings, they can remove
`$(ImplicitUsings)` from the `.csproj` completely or remove specific
`@(Using)` items:

    <ItemGroup>
      <Using Remove="Android.App" />
    </ItemGroup>
jonathanpeppers added a commit to jonathanpeppers/xamarin-android that referenced this issue Aug 23, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features
e42680b 
Context: dotnet/sdk#19521
Fixes: dotnet#6075
Fixes: dotnet#6076

We need to make two sets of changes for C# 10:

1. Support "global usings". Our .NET 6 templates should have no
   `using` statements at the top of `.cs` files.
2. Use `$(Nullable)` `enable` by default in project templates.

To test this, our .NET 6 MSBuild tests use `Nullable=enable` and
`ImplicitUsings=enable` by default and do not include `using`
statements in `.cs` files.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests. The
"legacy" Xamarin.Android tests will use the original file.

Our default `global using` are:

    global using global::Android.App;
    global using global::Android.Widget;
    global using Bundle = global::Android.OS.Bundle;

The last one is intentionally not bringing in `Android.OS`, because
`Android.OS.Environment` would conflict with `System.Environment`.

So `AutoImport.props` should become:

    <ItemGroup Condition=" '$(TargetPlatformIdentifier)' == 'android' and ('$(ImplicitUsings)' == 'true' or '$(ImplicitUsings)' == 'enable') ">
      <Using Include="Android.App" />
      <Using Include="Android.Widget" />
      <Using Include="Android.OS.Bundle" Alias="Bundle" />
    </ItemGroup>

So these items are present at the time `.csproj` files are evaluated.

Any templates will add:

    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>

If users want to configure these settings, they can remove
`$(ImplicitUsings)` from the `.csproj` completely or remove specific
`@(Using)` items:

    <ItemGroup>
      <Using Remove="Android.App" />
    </ItemGroup>
jonathanpeppers added a commit to jonathanpeppers/xamarin-android that referenced this issue Aug 23, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features
218a708 
Context: dotnet/sdk#19521
Fixes: dotnet#6075
Fixes: dotnet#6076

We need to make two sets of changes for C# 10:

1. Support "global usings". Our .NET 6 templates should have no
   `using` statements at the top of `.cs` files.
2. Use `$(Nullable)` `enable` by default in project templates.

To test this, our .NET 6 MSBuild tests use `Nullable=enable` and
`ImplicitUsings=enable` by default and do not include `using`
statements in `.cs` files.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests. The
"legacy" Xamarin.Android tests will use the original file.

Our default `global using` are:

    global using global::Android.App;
    global using global::Android.Widget;
    global using Bundle = global::Android.OS.Bundle;

The last one is intentionally not bringing in `Android.OS`, because
`Android.OS.Environment` would conflict with `System.Environment`.

So `AutoImport.props` should become:

    <ItemGroup Condition=" '$(TargetPlatformIdentifier)' == 'android' and ('$(ImplicitUsings)' == 'true' or '$(ImplicitUsings)' == 'enable') ">
      <Using Include="Android.App" />
      <Using Include="Android.Widget" />
      <Using Include="Android.OS.Bundle" Alias="Bundle" />
    </ItemGroup>

So these items are present at the time `.csproj` files are evaluated.

Any templates will add:

    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>

If users want to configure these settings, they can remove
`$(ImplicitUsings)` from the `.csproj` completely or remove specific
`@(Using)` items:

    <ItemGroup>
      <Using Remove="Android.App" />
    </ItemGroup>
jonpryor pushed a commit that referenced this issue Aug 25, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features (#6118)
7fb7c81 
Fixes: #6075
Fixes: #6076

Context: dotnet/sdk#19521

We need to make two sets of changes for C# 10:

 1. Support ["global usings"][0]. Our .NET 6 templates should have no
    `using` statements at the top of `.cs` files.

 2. Set `$(Nullable)`=enable by default in project templates, i.e.
    enable [C#8 nullable reference types][1] by default.

To test this, our .NET 6 MSBuild tests use `$(Nullable)`=enable and
`$(ImplicitUsings)`=enable by default and do not include `using`
statements in `.cs` files.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests.
The "legacy" Xamarin.Android tests will use the original file.

Our default `global using` are:

	global using global::Android.App;
	global using global::Android.Widget;
	global using Bundle = global::Android.OS.Bundle;

The last one is intentionally not bringing in `Android.OS`, because
`Android.OS.Environment` would conflict with `System.Environment`,
and the `System` namespace will be in `@(Using)` by default.

`AutoImport.props` should become:

	<ItemGroup Condition=" '$(TargetPlatformIdentifier)' == 'android' and ('$(ImplicitUsings)' == 'true' or '$(ImplicitUsings)' == 'enable') ">
	  <Using Include="Android.App" />
	  <Using Include="Android.Widget" />
	  <Using Include="Android.OS.Bundle" Alias="Bundle" />
	</ItemGroup>

so that these `using`s are present at the time `.csproj` files are
compiled.

Any templates will add:

	<Nullable>enable</Nullable>
	<ImplicitUsings>enable</ImplicitUsings>

If users want to configure these settings, they can remove
`$(ImplicitUsings)` from the `.csproj` completely, or remove specific
`@(Using)` items:

	<ItemGroup>
	  <Using Remove="Android.App" />
	</ItemGroup>

[0]: https://github.com/dotnet/csharplang/blob/b89d4c934041db923f7238b1427cd5f3ae71ed4b/proposals/csharp-10.0/GlobalUsingDirective.md#global-using-alias-directives
[1]: https://docs.microsoft.com/en-us/dotnet/csharp/nullable-references
jonathanpeppers added a commit that referenced this issue Aug 25, 2021
@jonathanpeppers
[One .NET] support latest C# 10 language features (#6118)
5e730fc 
Fixes: #6075
Fixes: #6076

Context: dotnet/sdk#19521

We need to make two sets of changes for C# 10:

 1. Support ["global usings"][0]. Our .NET 6 templates should have no
    `using` statements at the top of `.cs` files.

 2. Set `$(Nullable)`=enable by default in project templates, i.e.
    enable [C#8 nullable reference types][1] by default.

To test this, our .NET 6 MSBuild tests use `$(Nullable)`=enable and
`$(ImplicitUsings)`=enable by default and do not include `using`
statements in `.cs` files.

I've made a new `MainActivity.cs` for our .NET 6 MSBuild tests.
The "legacy" Xamarin.Android tests will use the original file.

Our default `global using` are:

	global using global::Android.App;
	global using global::Android.Widget;
	global using Bundle = global::Android.OS.Bundle;

The last one is intentionally not bringing in `Android.OS`, because
`Android.OS.Environment` would conflict with `System.Environment`,
and the `System` namespace will be in `@(Using)` by default.

`AutoImport.props` should become:

	<ItemGroup Condition=" '$(TargetPlatformIdentifier)' == 'android' and ('$(ImplicitUsings)' == 'true' or '$(ImplicitUsings)' == 'enable') ">
	  <Using Include="Android.App" />
	  <Using Include="Android.Widget" />
	  <Using Include="Android.OS.Bundle" Alias="Bundle" />
	</ItemGroup>

so that these `using`s are present at the time `.csproj` files are
compiled.

Any templates will add:

	<Nullable>enable</Nullable>
	<ImplicitUsings>enable</ImplicitUsings>

If users want to configure these settings, they can remove
`$(ImplicitUsings)` from the `.csproj` completely, or remove specific
`@(Using)` items:

	<ItemGroup>
	  <Using Remove="Android.App" />
	</ItemGroup>

[0]: https://github.com/dotnet/csharplang/blob/b89d4c934041db923f7238b1427cd5f3ae71ed4b/proposals/csharp-10.0/GlobalUsingDirective.md#global-using-alias-directives
[1]: https://docs.microsoft.com/en-us/dotnet/csharp/nullable-references
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Area: App+Library Build Issues when building Library projects or Application projects.
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[One .NET] support latest C# 10 language features jonathanpeppers/xamarin-android
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@jonpryor @jpobst @mhutch @jonathanpeppers