[generator] Make warning and error messages localizable. (#689)

Context: dotnet/android@0342fe5

Adds infrastructure to make the `Java.Interop` repository localizaable,
and rebases `generator` to work on this infrastructure.

Future PR's will make additional assemblies work on this infrastructure.

~~ Approach ~~

Create a single `Java.Interop.Localization.dll` assembly that will be
referenced by all localizable assemblies.  This approach allows us to
have a single set of `.xlf` files to worry about providing to
translators, instead of a separate set for `generator`, `class-parse`,
`ApiXmlAdjuster`, etc.

The downside to this approach is that if you only wanted to ship
`generator.exe` you would be shipping the messages for the entire repo.
Given that our use case is to ship all tools together, and that we
won't have a ton of messages, this seems like an acceptable tradeoff.
(`generator` contains the most messages, and with this commit
`Java.Interop.Localization.dll` is ~9KB.)

Currently we only plan to localize the tools used on desktop to build
bindings.  If we localize assemblies that run on device in the future,
we would most likely make a separate "run-time" set, as we wouldn't
want to ship e.g. `generator` messages on a device.

~~ Usage ~~

To create a new translatable string (all assemblies):

  * Open `Java.Interop.Localization.Resources.resx` in an IDE.
  * Enter the string lookup key, string value, and any notes for
    translators.
  * The string can now be retrieved via
    `Java.Interop.Localization.Resources.MyStringKey`.

~~ Generator Usage ~~

To use the string in `generator.exe`:

  * Create a new static member in `Utilities/Report.cs` that assigns
    a build code to the string.

        public static LocalizedMessage WarningUnknownReturnType => new LocalizedMessage (8700, Java.Interop.Localization.Resources.Generator_BG8700);

  * Use `Report.LogCodedWarning()` or `Report.LogCodedError()` to
    create an `MSBuild` formatted build warning/error.

        Report.LogCodedError (Report.ErrorFailedToProcessEnumMap);
    
    Overloads are available that take exceptions, file/line/col info,
    and `string.Format()` parameters.

.gitattributes

@@ -19,6 +19,8 @@
 *.Designer.cs	eol=crlf
 
 *.cs	text
+*.resx	text
+*.xlf	text
 *.xml	text
 *.md	text
 Makefile	eol=lf

Directory.Build.props

@@ -5,6 +5,12 @@
     <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
     <_OutputPath>$(MSBuildThisFileDirectory)bin\Build$(Configuration)\</_OutputPath>
   </PropertyGroup>
+
+  <PropertyGroup>
+    <XlfLanguages>cs;de;es;fr;it;ja;ko;pl;pt-BR;ru;tr;zh-Hans;zh-Hant</XlfLanguages>
+    <UpdateXlfOnBuild Condition="'$(RunningOnCI)' != 'true'">true</UpdateXlfOnBuild>
+  </PropertyGroup>
+
   <Import
       Project="$(MSBuildThisFileDirectory)Configuration.Override.props"
       Condition="Exists('$(MSBuildThisFileDirectory)Configuration.Override.props')"

Java.Interop.sln

@@ -97,6 +97,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Xamarin.SourceWriter", "src
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Xamarin.SourceWriter-Tests", "tests\Xamarin.SourceWriter-Tests\Xamarin.SourceWriter-Tests.csproj", "{6CF94627-BA74-4336-88CD-7EDA20C8F292}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Java.Interop.Localization", "src\Java.Interop.Localization\Java.Interop.Localization.csproj", "{998D178B-F4C7-48B5-BDEE-44E2F869BB22}"
+EndProject
 Global
 	GlobalSection(SharedMSBuildProjectFiles) = preSolution
 		src\Java.Interop.NamingCustomAttributes\Java.Interop.NamingCustomAttributes.projitems*{58b564a1-570d-4da2-b02d-25bddb1a9f4f}*SharedItemsImports = 5
@@ -269,6 +271,10 @@ Global
 		{6CF94627-BA74-4336-88CD-7EDA20C8F292}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{6CF94627-BA74-4336-88CD-7EDA20C8F292}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{6CF94627-BA74-4336-88CD-7EDA20C8F292}.Release|Any CPU.Build.0 = Release|Any CPU
+		{998D178B-F4C7-48B5-BDEE-44E2F869BB22}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{998D178B-F4C7-48B5-BDEE-44E2F869BB22}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{998D178B-F4C7-48B5-BDEE-44E2F869BB22}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{998D178B-F4C7-48B5-BDEE-44E2F869BB22}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -315,6 +321,7 @@ Global
 		{F46EDFA5-C52A-4F0C-B5A2-5BB67E0D8C74} = {C8F58966-94BF-407F-914A-8654F8B8AE3B}
 		{C5B732C8-7AF3-41D3-B903-AEDFC392E5BA} = {0998E45F-8BCE-4791-A944-962CD54E2D80}
 		{6CF94627-BA74-4336-88CD-7EDA20C8F292} = {271C9F30-F679-4793-942B-0D9527CB3E2F}
+		{998D178B-F4C7-48B5-BDEE-44E2F869BB22} = {0998E45F-8BCE-4791-A944-962CD54E2D80}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {29204E0C-382A-49A0-A814-AD7FBF9774A5}

NuGet.Config

@@ -4,7 +4,11 @@
      - NUnit.Console
      - csc.exe
 -->
-<configuration>  
+<configuration>
+  <packageSources>
+    <!-- For XliffTasks -->
+    <add key="dotnet-eng" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-eng/nuget/v3/index.json" protocolVersion="3" />
+  </packageSources>
   <config>
     <add key="globalPackagesFolder" value="packages" />
   </config>

src/Java.Interop.Localization/Java.Interop.Localization.csproj

@@ -0,0 +1,26 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="XliffTasks" Version="1.0.0-beta.20206.1" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Compile Update="Resources.Designer.cs">
+      <DesignTime>True</DesignTime>
+      <AutoGen>True</AutoGen>
+      <DependentUpon>Resources.resx</DependentUpon>
+    </Compile>
+  </ItemGroup>
+
+  <ItemGroup>
+    <EmbeddedResource Update="Resources.resx">
+      <Generator>PublicResXFileCodeGenerator</Generator>
+      <LastGenOutput>Resources.Designer.cs</LastGenOutput>
+    </EmbeddedResource>
+  </ItemGroup>
+
+</Project>