Also expose the awaiters to Microsoft.Test.Apex.VisualStudio

Fixes #12378

Expose a special CodeActionOperation so users can navigate to document positions as part of applying a code action.

* Fixes rude error reporting for lifted implicit value parameters

* Allow null

We're going to do some quality/perf testing (and possibly full on dogfooding) first to get
more confidence about this before having them be on by default.