This reverts commit f4a419b2, reversing
changes made to 23e5b1c1.

This reverts commit 0cff1ac1, reversing
changes made to faba4b44.

We had a workaround in InvisibleEditor.cs where we would deal with a
case where the IVsHierarchy we had was a different IVsHierarchy than
was registered with the solution manager in Visual Studio. This was a
workaround for an old behavior in our CPS-based project system where
if you were multi-targeting, each target got it's own IVsHierarchy
wrapper which wrapped the real one. That hasn't been the case for some
time so we can delete this now.

fixes #43495

Fixes https://dev.azure.com/devdiv/DevDiv/_workitems/edit/1155506

Fixes #46255

* Test compositions

* Eliminate TestExportProvider

* Fixes and caching

* Debugger proxies

* Scopes

* Feedback and more fixes

* RemoteHostOptions

* Throw without timeout on invalid thread switches

* EventCollectorTests requires a main thread

Bump versions of System.Collections.Immutable and System.Reflection.Metadata to consume the new function pointer metadata changes.

Replacing ILanguageServerProtocol with AbstractRequestHandlerProvider.
Refactoring common Extensions method code into generic helpers.

Remove wait for out of process start from OnLoadedAsync as it has not cancellation token.  The wait will instead occur in ActivateAsync with cancellation

Added XAML LSP shims by introducing ILanguageServerProtocol and adding an optional Language parameter to the ExportLspMethodHandlerAttribute so that XAML can export its own LSP handlers.
Added a few extension methods to make dealing with TextDocuments easier.

Co-authored-by: NCyrusNajmabadi <cyrus.najmabadi@gmail.com>