audio: Add pause, resume, and standby stream operations

Clarify and verify in VTS that the data FMQ of StreamDescriptor
is a transient buffer. The consumer must always read its entire
contents. This is the same behavior as in the HIDL HAL.

Define the state machine for streams and the set of commands for
transferring between states.

Clarify and verify in VTS that the frame counter of the
observable position must never be reset.

Implement commands for the synchronous I/O case.

Refactor stream test logic to simplify testing of state
transitions.

Bug: 205884982
Test: atest VtsHalAudioCoreTargetTest
Change-Id: Ibed7f4c3e77852863714f1910112f664b32d5897