SDK / exoplayer

Some Player methods operate relative to existing indices in the
playlist (add,remove,move,seek). As these operations may be issued
from a place with a stale playlist (e.g. a controller that sends
a command while the playlist is changing), we have to handle out-
of-bounds indices gracefully. In most cases this is already
documented and implemented correctly. However, some cases are not
documented and the existing player implementations don't handle
these cases consistently (or in some cases not even correctly).

PiperOrigin-RevId: 495856295
(cherry picked from commit a1954f7e)