SDK / exoplayer

This is achieved by only triggering one message at a time. After
triggering a message we send another to ourselves to know when the
following message can be triggered.

Other required changes:
 - The messages need to be sorted correctly (by time and creation order)
 - To prevent deadlocks when one thread is waiting for another,
   we need to add new method to Clock to indicate that the current
   thread is about to wait. This then allows us to trigger messages
   from other threads in FakeClock.
 - AnalyticsCollectorTest needed some adjustments:
   - onTimelineChanged now deterministically arrives after the initial
     timline is already known, so some of the period information changes
     from window only to full period info.
   - The playlistOperations test suffers from a bug that the first frame
     is rendered too early and that's why we now get additional events.

PiperOrigin-RevId: 353877832