Fix disconnect during init logging

Summary:
When a client disconnects while it's still initialising, we get a critical error.
But this is expected to happen now and again, so adding a specific error for it, and handling it accordingly.
It doesn't change the control flow, just the logging.

Reviewed By: nikoant

Differential Revision: D32794062

fbshipit-source-id: cf27fb9c345aa6369d338838a46e75a6b7afde41

desktop/flipper-common/src/index.tsx

@@ -34,6 +34,7 @@ export {
   CancelledPromiseError,
   UserUnauthorizedError,
   UserNotSignedInError,
+  NoLongerConnectedToClientError,
   isConnectivityOrAuthError,
   isError,
   isAuthError,