See methods like TryGetSourceGeneratedDocumentFromUriAsync. We have situations where we have to deal with the Uris of generated documents, and those Uris contain yummy information, but we can't get at it. We should expose some helpers around Roslyns SourceGeneratedDocumentUri to make this nicer.

See also where we check the Uri scheme for "roslyn-source-generated", as it's changed at least once since I started working on cohosting :)