[One .NET] fixes for System.* PackageReference

[jonathanpeppers]

Context: dotnet/maui#1309 (comment)

dotnet/maui projects are failing to build after adding new ASP.NET
assemblies for BlazorWebView:

error XABLD7024: System.IO.IOException: The process cannot access the file 'D:\a\1\s\src\Controls\samples\Controls.Sample.SingleProject\obj\Release\net6.0-android\android\lz4\System.Runtime.CompilerServices.Unsafe.dll.lz4' because it is being used by another process. [D:\a\1\s\src\Controls\samples\Controls.Sample.SingleProject\Maui.Controls.Sample.SingleProject.csproj]
error XABLD7024:    at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath) [D:\a\1\s\src\Controls\samples\Controls.Sample.SingleProject\Maui.Controls.Sample.SingleProject.csproj]
error XABLD7024:    at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost) [D:\a\1\s\src\Controls\samples\Controls.Sample.SingleProject\Maui.Controls.Sample.SingleProject.csproj]
error XABLD7024:    at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share) [D:\a\1\s\src\Controls\samples\Controls.Sample.SingleProject\Maui.Controls.Sample.SingleProject.csproj]
error XABLD7024:    at Xamarin.Android.Tasks.AssemblyCompression.Compress(AssemblyData data, String outputDirectory) [D:\a\1\s\src\Controls\samples\Controls.Sample.SingleProject\Maui.Controls.Sample.SingleProject.csproj]
error XABLD7024:    at Xamarin.Android.Tasks.BuildApk.<AddAssemblies>g__CompressAssembly|142_1(ITaskItem assembly, <>c__DisplayClass142_0& ) [D:\a\1\s\src\Controls\samples\Controls.Sample.SingleProject\Maui.Controls.Sample.SingleProject.csproj]
error XABLD7024:    at Xamarin.Android.Tasks.BuildApk.AddAssemblies(ZipArchiveEx apk, Boolean debug, Boolean compress, IDictionary`2 compressedAssembliesInfo) [D:\a\1\s\src\Controls\samples\Controls.Sample.SingleProject\Maui.Controls.Sample.SingleProject.csproj]
error XABLD7024:    at Xamarin.Android.Tasks.BuildApk.ExecuteWithAbi(String[] supportedAbis, String apkInputPath, String apkOutputPath, Boolean debug, Boolean compress, IDictionary`2 compressedAssembliesInfo) [D:\a\1\s\src\Controls\samples\Controls.Sample.SingleProject\Maui.Controls.Sample.SingleProject.csproj]
error XABLD7024:    at Xamarin.Android.Tasks.BuildApk.RunTask() [D:\a\1\s\src\Controls\samples\Controls.Sample.SingleProject\Maui.Controls.Sample.SingleProject.csproj]
error XABLD7024:    at Microsoft.Android.Build.Tasks.AndroidTask.Execute() in /Users/builder/azdo/_work/1/s/xamarin-android/external/xamarin-android-tools/src/Microsoft.Android.Build.BaseTasks/AndroidTask.cs:line 17 [D:\a\1\s\src\Controls\samples\Controls.Sample.SingleProject\Maui.Controls.Sample.SingleProject.csproj]

Which appears to be due to a duplicate assembly:

Task GenerateCompressedAssembliesNativeSourceFiles
...
Skipping duplicate assembly: obj\Release\net6.0-android\android-x86\linked\System.Runtime.CompilerServices.Unsafe.dll

If you go earlier in the log:

Task ProcessAssemblies
...
Android ABI not found for: obj\Release\net6.0-android\android-arm64\linked\System.Runtime.CompilerServices.Unsafe.dll
Android ABI not found for: obj\Release\net6.0-android\android-x86\linked\System.Runtime.CompilerServices.Unsafe.dll

This is happening because %(RuntimeIdentifier) is blank?

I could reproduce this in a test, but only after adding a complicated
set of @(PackageReference) to an app project.

I believe what is happening is:

• We have a @(PackageReference) to a System.* assembly that is also
  in the Mono runtime packs: Microsoft.NETCore.App.Runtime.*
• If the @(PackageReference) version is newer than
  Microsoft.NETCore.App.Runtime.*, then it will be preferred over
  the other.

In this case, %(RuntimeIdentifier) is blank on the
@(PackageReference). It appears to only be set by runtime packs.

Solution:

• Set @(ResolvedFileToPublish.RuntimeIdentifier) to
  $(RuntimeIdentifier) if it is blank.

This solved all my warning messages and my test case now compiles.