[VS Code] [Cohosting] Closing html tags don't get auto-inserted

Right now in VS Code, there is a hook to `textDocument/didChange` that uses the `razor/languageQuery` endpoint to provide close tag insertion when typing `>`.

We should look to move this to onAutoInsert, which Roslyn already have a feature to emulate in VS Code. Hopefully just a matter of porting the endpoint in Razor, and ensuring we get the requests (probably limited to .cs files right now)