Camera2: Move still capture processing to separate thread.

To avoid stalling HAL when it queues up new buffers for still capture,
process still captures in a separate thread. Also move Camera2Heap to
its own class so it can be used by the CaptureProcessor.

Bug: 6243944
Change-Id: Id38e2a52367c0985812fcd4fd9af3ef90beef43f
6 files changed