SDK / exoplayer

Some commands may be asynchronous and subsequent commands need to
wait for them to complete before running. This change updates the
queue to use (and listen to) Futures instead of calling Runnables
directly. The commands are currently still added as Runanbles
though, so this change is a no-op.

Also moves the permission check in MediaSessionImpl to before
queueing the command because the permission should be check at
the time of calling the method.

When executing the comamnds in the queue, we need to be careful
to avoid recursion in the same thread (which happens when both
the Future is immediate and running on the correct thread already).
To avoid recursion, we detect this case and loop the commands
instead.

Issue: androidx/media#85
PiperOrigin-RevId: 461827264
(cherry picked from commit dee80788)