Fix FormattingContext disposal

[davidwengier]

From a conversation on Teams. FormattingContext is disposable because it owns a workspace, but it also gets non-destructively mutated so it's unclear as to whether the disposal was working as intended, and unclear to consumers what needed to happen. Upon review of the code, this PR:

• Moves workspace ownership to the caller of the formatting code, so its disposal is clear
• Makes AdhocWorkspaceFactory shared code, because it did the same thing in OOP and LSP server
• Adds IHostServicesProvider to OOP, because thats the thing that was actually different between OOP and LSP server
• Random cleanup of some related things

[alexgav]

LGTM, my only thought is - do we still need the Provider if there is 1:1 mapping between them? Is there a lot of value in lazily creating the workspace via the provider?

[DustinCampbell]

Thanks for the clean up! The disposal and ownership of the workspace is much cleaner, though I think the IDisposable contract in AdhocWorkspaceProvider can be tightened up a bit more.

[davidwengier]

do we still need the Provider if there is 1:1 mapping between them?

Right now all of our tests pass if we don't use any of the host services provider stuff, and if VA Code formatting works then I don't know why we couldn't just have the code be new AdhocWorkspace() but I also don't know if I trust our current tests to actually make that determination, so I didn't scratch too far below the surface.

[davidwengier]

Thank you for the excellent PR feedback! I have moved the workspace and document creation down even lower, so FormattingContext has nothing to do with it now. Much nicer IMO. Should have scratched the surface just a little bit more :)

[DustinCampbell]

Very nice! I'm not sad to see IAdhocWorkspaceFactory removed. 😄