We currently clear all pending messages, including the one that flushes
pending commands to the MediaSession. To ensure all commands that have
been called before controller.release() are still sent, we can manually
trigger the flush message from the release call.
Related to handling the final flush because disconnecting the controller,
MediaSessionStub didn't post the removal of the controller to the
session thread, creating a race condition between removing the controller
and actually handling the flush.
Issue: androidx/media#99
PiperOrigin-RevId: 462342860
(cherry picked from commit ee209690cb54fc800cf3a213f5075c9aaf51463c)
29246fb1b2