[dotnet test] Add androidtest project template and dotnet run instrumentation support

[jonathanpeppers]

Context: #10683

Add a new androidtest .NET project template that creates an Android test project using MSTest with Microsoft.Testing.Platform. The template includes a TestInstrumentation class that runs tests via am instrument and reports results (passed/failed/skipped) back through Android's instrumentation protocol.

Add --instrument option to Microsoft.Android.Run so dotnet run can launch test projects via am instrument -w instead of am start.

Fix an issue where NuGet packages like MSTest add assemblies as both properly-resolved publish assets (with DestinationSubPath metadata) and as None items (without DestinationSubPath) that flow into _SourceItemsToCopyToPublishDirectory. When NuGet conflict resolution arbitrarily picks the None-based copy, the assembly loses its DestinationSubPath and TargetPath metadata, causing it to either be missing from the APK or deployed to the wrong directory on device. The fix conditionally removes only items without DestinationSubPath, then re-adds any assemblies that were completely stripped with a cleared TargetPath so that downstream targets (ProcessAssemblies, FastDeploy) can set the correct per-architecture paths.

Changes:

• New androidtest template under src/Microsoft.Android.Templates/
• New GetAndroidInstrumentationName MSBuild task to resolve the instrumentation runner class from AndroidManifest.xml
• Updated Microsoft.Android.Sdk.Application.targets to pass --instrument when EnableMSTestRunner is true
• Added AdbHelper class to Microsoft.Android.Run for shared adb process management
• Added --instrument CLI option to Microsoft.Android.Run/Program.cs
• Fixed _ComputeFilesToPublishForRuntimeIdentifiers to preserve properly-resolved publish assets and recover missing assemblies
• Added DotNetNewAndroidTest device integration test

TODO:

• In a future PR, add support for dotnet test end-to-end.