There are two sets of listeners in ExoPlayerImpl at the moment,
which can be merged together to use a single ListenerSet. This has
the added advantage that the events that were previously sent
through the ArraySet get additional guarantees provided by ListenerSet
(e.g. correct event ordering and onEvents triggered).
Also add missing constants for onEvents to ensure all Player.Listener
methods have an corresponding constant.
#minor-release
PiperOrigin-RevId: 427415349
1baac238e1