SDK / exoplayer

Ensure listener invocations use final state variable.

The MediaControllerImplBase listener invocations currently use the
class member state that can change if one of the listener method
implementations changes the state recursively.

Updating the listener invocations to use a final local variable
ensures all listeners get consistent updates.

PiperOrigin-RevId: 487503373
(cherry picked from commit 33bea391)