Make finding checksum async

[tmat]

When we retrieve an object for Text checksum in DocumentStateChecksums we used a trick to avoid making Find asynchronous and save Task allocations. We placed DocumentState to the result instead of the expected SourceText and retrieved the actual SourceText instance later on, when we were in async context. We can avoid the Task allocations by using ValueTask, remove this special casing and simplify SolutionAsset implementation.

Add nullable annotations.

Move methods from Microsoft.CodeAnalysis.Remote.Shared.Extensions to TestUtils as they are only used for testing.

Remove SolutionAssetManager and RemoteHostPanel. They were only used for experimenting and are no longer needed.

[sharwell]

20/27 files reviewed so far

[tmat]

@sharwell Would we want TextDocumentState.GetTextAsync to use ValueTask to avoid Task allocation when it completes synchronously?

[sharwell]

Would we want TextDocumentState.GetTextAsync to use ValueTask to avoid Task allocation when it completes synchronously?

The overwhelming use of this method enters through TextDocument.GetTextAsync. Since that implementation delegates (as opposed to wrapping the call in its own async method), there will be an unavoidable task allocation regardless of the return type in TextDocumentState.

FWIW, TextDocument.GetTextAsync has definitely shown up on my list of async methods that would benefit from ValueTask<T>. The only reason it isn't converted is we need to find a pattern for handling public APIs.

[tmat]

The overwhelming use of this method enters through TextDocument.GetTextAsync. Since that implementation delegates (as opposed to wrapping the call in its own async method), there will be an unavoidable task allocation regardless of the return type in TextDocumentState

That's true, but making TextDocumentState.GetTextAsync would at least avoid some allocations until we figure out the new public API.

[tmat]

@dotnet/roslyn-ide PTAL