SourceGenerators folder

1. The Uno.UI.SourceGenerator project is referenced by XamlGenerationTests.
2. During compilation XAML within XamlGenerationTests will be code generated. It's worth looking at XamlGenerationTests/XamlGenerationTests.csproj for insights on how this works, specifically TargetFrameworksCI and the PackageReferences.
3. If this fails, then the CI build will fail.

Thus XamlGenerationTests is the test suite for Uno.UI.SourceGenerator and is typically where tests should be added.