Camera2: Basic ZSL and precapture trigger support.

- Add capture sequencer to control still image capture process
- Use precapture trigger for standard capture in sequencer
- Add infrastructure for reprocessing streams
- Add ZSL processor to maintain ZSL queue
- Add ZSL capture sequence to sequencer

This patch sets up ZSL mode and precapture triggers.

For now, to enable zsl mode, set the system property camera.zsl_mode
to 1.

Bug: 6243944

Change-Id: Icf8cb1a83a7c11a152a11007c8f3c54f8ea1c70c