Use pause signaling to halt a video call when data limit is reached.

This proved to be problematic as the InCallUI is the only place where
we would previously get a pause signal.  Added a VideoPauseTracker
class which is responsible for tracking the source of pause requests and
ensuring that the video is only paused on the first request, and only
resumed on the last resume request.

Added some new logic to ImsVideoCallProviderWrapper to support receiving
pause and resume requests from other sources, and to ensure that requests
to pause or resume use the VideoPauseTracker to determine if the pause
or resume should actually be passed along to the modem.

Test: manual
Bug: 30760683
Change-Id: Id54b2a955745132ab09feb01b5c961f6115ef3df