Bug 1870499 - Make sure ContinueDoNotifyListener is called immediately during release a=diannaS

The causes of the runnable loop are as follows:
1. In Release we have a special case to make sure OnStart&OnStop are always
   called. We do this by dispatching a runnable that calls DoNotifyListener.
2. DoNotifyListener is called, then the reference to the channel is again
   dropped. But at this point only OnStartRequest was called, and
   ContinueDoNotifyListener was added to mEventQ. That means another
   runnable would be dispatched.

While the loop was broken in the previous patch, we still want to ensure
OnStopRequest is called before the channel is released, so this patch
adds an argument to DoNotifyListener to select whether ContinueDoNotifyListener
should be called synchronously or dispatched to mEventQ.

Original Revision: https://phabricator.services.mozilla.com/D202798

Differential Revision: https://phabricator.services.mozilla.com/D204063