[Video Capture]: allow client to enable face detection

On certain devices, enabling face detection will trigger tuning
to provide better exposure around the face area. So expose
this configuration to allow an application to enable it if
it wants to.

Currently, this is only supported by Android Camera2 driver.

Bug: b/110420728
Test: Build
Change-Id: I6a512740a0bc06fb1b6f6352dd2f65ce6830bf02
Reviewed-on: https://chromium-review.googlesource.com/c/1110268
Commit-Queue: Peter Qiu <zqiu@chromium.org>
Reviewed-by: Emircan Uysaler <emircan@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603979}
9 files changed