Update to Avalonia 11 preview 8

[danipen]

Update the codebase to Avalonia 11 preview 8.

[danipen]

Unit test project is not compiling due to internal API visibility. We probably need to migrate these tests to the headless platform.

[danipen]

cc/ @maxkatz6 @grokys @danwalmsley @Gillibald @kekekeks

[maxkatz6]

On my way to migrate these tests AvaloniaUI/Avalonia#11146

[maxkatz6]

@danipen done, but we probably need to wait until AvaloniaUI/Avalonia#11169 is merged at least. It should be fine to target preview7 in the main project and nightly in the tests project. As necessary changes affect only tests.

[danipen]

@maxkatz6 should the tests pass green? I'm getting some errors:

Message
    System.InvalidOperationException : Avalonia Headless platform has failed to initialize.
Stack Trace: 
<>c__DisplayClass19_0.<StartNew>b__0() line 94
--- End of stack trace from previous location ---
HeadlessUnitTestSession.StartNew(Type entryPointType) line 111
HeadlessUnitTestSession.GetOrStartForAssembly(Assembly assembly) line 142
AvaloniaTestAttribute.Wrap(TestCommand command) line 20
SimpleWorkItem.MakeTestCommand()
SimpleWorkItem.PerformWork()

And also:

Message
    System.InvalidOperationException : Setup was already called on one of AppBuilder instances
Stack Trace: 
AppBuilder.Setup() line 287
AppBuilder.SetupWithoutStarting() line 187
<>c__DisplayClass19_0.<StartNew>b__0() line 90
--- End of stack trace from previous location ---
HeadlessUnitTestSession.StartNew(Type entryPointType) line 111
HeadlessUnitTestSession.GetOrStartForAssembly(Assembly assembly) line 142
AvaloniaTestAttribute.Wrap(TestCommand command) line 20
SimpleWorkItem.MakeTestCommand()
SimpleWorkItem.PerformWork()```

[maxkatz6]

@danipen yes, it was green locally, maybe wrong build number. I will check.

[danipen]

BTW loving this change, unit tests get much more simple!

[danipen]

yes, it was green locally, maybe wrong build number. I will check.

@maxkatz6 did you take a look into it?

[maxkatz6]

Yes, non-UI tests in this repo are using Dispatcher, which is uses before proper headless initialization, caching incorrect dispatcher implementation. I need to figure out how to avoid it without affecting this code base too much.

[danipen]

@maxkatz6 any updates on this?

[maxkatz6]

@danipen done. Should be ready to merge as preview7 or preview8 or both.
Tests project references master branch as only that one has needed headless changes to support NUnit and more. But non-test code wasn't changed, it still preview7.

[Gillibald]

Let us target preview8 as that is the most recent version

[hez2010]

Hello, is there any chance of publishing a preview8 package on nuget?

[Gillibald]

https://www.nuget.org/packages/Avalonia.AvaloniaEdit/11.0.0-preview8

[hez2010]

Oops, I missed that one.
Thank you.