AddToWorkspace doesn't support source generators

[svick]

Consider the following code (where C:\code\roslyn-sdk is a path to checked out dotnet/roslyn-sdk):

var manager = new AnalyzerManager();
var analyzer = manager.GetProject(@"C:\code\roslyn-sdk\samples\CSharp\SourceGenerators\GeneratedDemo\GeneratedDemo.csproj");
AdhocWorkspace workspace = new AdhocWorkspace();
Project roslynProject = analyzer.AddToWorkspace(workspace);

foreach (var analyzerReference in roslynProject.AnalyzerReferences)
{
    Console.WriteLine(analyzerReference.FullPath);
}

This does not print anything; roslynProject.AnalyzerReferences is empty.

What I expect is that it prints references to source generator assemblies used by the project:

C:\Users\PetrOnderka\.nuget\packages\csvtextfieldparser\1.2.2-preview\lib\netstandard2.0\CsvTextFieldParser.dll
C:\Users\PetrOnderka\.nuget\packages\handlebars.net\1.10.1\lib\netstandard2.0\Handlebars.dll
C:\Users\PetrOnderka\.nuget\packages\newtonsoft.json\12.0.1\lib\netstandard2.0\Newtonsoft.Json.dll
C:\code\roslyn-sdk\artifacts\bin\SourceGeneratorSamples\Debug\netstandard2.0\SourceGeneratorSamples.dll

I plan to submit a PR that fixes this soon.

[daveaglick]

Cool! Never even considered adding analyzers and generators to the workspace, but if Roslyn tracks them it definitely makes sense to add them.