_IncludeGenerateTestingPlatformEntryPointIntoCompilation target is suspect

[Youssef1313]

• Using BeforeTargets="CoreCompile", in my experience, is buggy in most cases. We need to verify, but in many cases such targets end up running after _GenerateCompileDependencyCache so they are not included in the hash. This can cause weird incremental build issues. Usually BeforeCompile is a better hook. See [Bug]: Input file "*.CoreCompileInputs.cache" is newer than output file "*.pdb" dotnet/msbuild#8807 for example of the kind of issue this can cause.
• We should also consider running it before XamlPreCompile (important for WinUI), and potentially provide an extensibility so that people with special infrastructure can run the target earlier per their requirements.