We currently start a simple Thread to release AudioTracks
asynchronously. If many AudioTracks are released at the same
time, this may lead to OOM situations because we attempt to
create multiple new threads.
This can be improved by using a shared SingleThreadExecutor.
In the simple case of one simmultaneous release, it's exactly
the same behavior as before: create a thread and release it
as soon as it's done. For multiple simultanous releases we
get the advantage of sharing a single thread to avoid creating
more than one at the same time.
Issue: google/ExoPlayer#10057
PiperOrigin-RevId: 460698942
