SDK / exoplayer

Currently we don't remove the AnalyticsListeners registed to
SimpleExoPlayer after calling release. We didn't do this mainly
because there are messages triggered as part of the release that
still cause interesting events (e.g. decoderDisabled with the
final counters, final dropped counts etc).

However, we should fully release/remove the listeners once these
pending events are delivered to:
 1. Not leak listener implementations (e.g. if the listener is an
    Activity)
 2. Ensure we don't send future events that may cause listeners
    to unintentionally access released or nulled variables. This
    could happen for example if someone calls a player method
    after the player was released.
In addition, we can add a onPlayerReleased callback to
AnalyticsListener to allow implementations to clean themselves up
once all pending events are delivered.

PiperOrigin-RevId: 347434344