Changed setSyncTransaction to syncNextTransaction with callback logic.

Replaced setSyncTransation with syncNextTransaciton in BBQ. BBQ will
no longer take in transaction pointers but create transactions inside
of itself and invoke the callback when the transaction is ready.
Also added stopContinuousSyncTransction method to inform BBQ to cease
acquiring buffers into the transaction.

Test: go/wm-smoke.
Test: BLASTBufferQueueTest
Bug: 210714235.
Change-Id: I7103a95046d0251e5bdaec21b2741ff194f8e81e