Add standby mode for aaudio service stream.

When the stream is stopped, everything will remain open but just stop
writing data. But this will keep the DSP running and using power
until the stream is closed.
To resolve this issue, the solution is to put the stream into standby
mode so that the HAL can release the corresponding resource.
When the HAL releases the resource, the shared file descriptor will also
be released. In that case, when the stream is restarted, AAudioService
needs to recreate shared buffer and the client needs to replace the new
shared buffer.

Test: atest AAudioTests
Test: test_steal_exclusive
Bug: 201000721
Bug: 196394385
Bug: 167345722
Bug: 208619472
Change-Id: Ib4f98e7aee72c2e56acd7f2f0ac378a94ec26241