audio: Add non-blocking I/O stream operations

Introduce IStreamCallback interface for non-blocking I/O. Add 2
new stream states: TRANSFERRING and TRANSFER_PAUSED, and define
state machines for the async case. Add DrainMode as in previous
HAL versions.

Note that non-blocking input is not fully implemented because it
did not exist in previous HAL versions, and the corresponding
AudioInputFlag does not exist yet.

Enhance VTS state machine tests to allow waiting for an async
event.

Bug: 205884982
Test: atest VtsHalAudioCoreTargetTest
Change-Id: I0a18a6d930dee5941f769e08083817d41ff941e6