Use a separate thread to disconnect registered streams.

When the stream is torn down due to request from AudioFlinger, the
streams in shared mode will try to disconnect all registered streams in
the data callback thread. This will trigger stop all streams. When the
last registered stream is stopped, data callback thread will be joined.
That will cause a dead lock since the join thread is called from the
command thread when calling stop, while the stream is stopped by the
data callback thread.

To fix that issue, a separated thread is spawned to disconnect
registered streams so that the data callback thread can be joined
correctly.

Bug: 207408882
Test: repo steps in the bug
Test: atest AAudioTests
Change-Id: I317101818a49aa6750da544e35321f82b384748f