JsonRPC protocol epic issue #5490

Initialize request

• initialize request has debuggerProvider capability, which the server doesn't make use of at all. This is also because the server never sends client/launchDebugger and client/attachDebugger requests. Should we remove those requests for now?
• batchLoggingSupport is documented but not implemented both in Test Explorer and server. I think this should be removed from the documentation, until it's needed and implemented.
• Client capabilities documents attachmentsSupport, but Test Explorer actually sends attachmentsProvider (always sends it as true). The server doesn't care about either of the two. I think this can be removed altogether.
• Client capabilities documents callbackProvider, but this is not implemented both in TE and server.
• On TE side, multipleConnectionProvider is part of client capabilities. On server side, it's part of server capabilities. And is not documented in both.

Initialize response

• Both server and client has ProcessId as part of initialize response, which is not documented.
• The documented capabilities are experimental_multiRequestSupport and attachmentsProvider.
  • TODO for me: Validate how experimental_multiRequestSupport is used.
  • Both client and server use attachmentsSupport, not attachmentsProvider
  • supportsDiscovery, vstestProvider, multipleConnectionProvider are part of server capabilities on the server implementation, but not documented (well, vstestProvider is documented in an extension document, but no mentioned in the main one)

TODO: Review the rest. So far I reviewed only the initialize part.