* Adds nullability, removes dead code.

* Clean up RemoteHostClient exception and lifetime handling

* Nullables

* JsonRpcEx disposal cleanup

* Nullables

* Refactor abstract JsonRpcEx to sealed RemoteEndPoint

* Use RemoteEndPoint for ServiceHub services

* Move ctor

* Use RemoteEndPoint in ServiceHubRemoteHostClient

* Minor cleanup of log messages

* JsonRpcTargetOptions

* Use RemoteEndPoint in CodeLens, tests

* Inline Extensions.InvokeAsync methods into RemoteEndPoint

* Remove unnecessary invoke methods

* Unify exception handling

* Allow null arguments in remote invocation

* Simplify ClientDirectStream

* Fold ClientDirectStream and ServerDirectStream into RemoteEntryPoint

* Feedback

* Fix test