Rely on GetUsedAssemblyReferences

[stan-sz]

Following dotnet/roslyn#625 and https://learn.microsoft.com/en-us/dotnet/api/microsoft.codeanalysis.csharp.csharpcompilation.getusedassemblyreferences?view=roslyn-dotnet-4.3.0 refactor ReferenceTrimmer to use that API. The dotnet/sdk#10414 might be of a great help here.

Another option is to write a simple analyzer that will dump the result of GetUsedAssemblyReferences to a known file and ReferenceTrimmer would pick it up to perform it's action. The analyzer could be hooked up via this package nuget's .props.