This inheritance is really confusing because ExoPlayerImpl is not
a full Player interface implementation. It also claims to be an
ExoPlayer implementation in the Javadoc which isn't true in its
current state.
Removing the inheritance also allows to clean up some unused methods.
PiperOrigin-RevId: 411756963
Where this introduced an inconsistency (e.g. assigning to something
called `windowIndex`), I generally renamed the transitive closure of
identifiers to maintain consistency (meaning this change is quite
large). The exception is code that interacts with Timeline and Window
directly, where sometimes I kept the 'window' nomenclature.
#minor-release
PiperOrigin-RevId: 407040052
Only deprecated references remain.
Usages of the deprecated methods will be migrated in a follow-up change.
#minor-release
PiperOrigin-RevId: 405927141
