- Updated the a `VisualStudioWorkspaceAccessor` API in windows to enable the factory to retrieve a workspace given a text buffer.
- Added a way to add test services to `AdhocWorkspace` so we can test against services being retrieved from a `Workspace`. This will be much more common once we rely on services coming from `TextBuffer`s in our other tooling pieces.
- Added tests for the default workspace provider.
#1989