Merge "Camera: Clarify doc for registerAvailabilityCallback" into tm-dev am: 837979c6 am: 41e5c63e

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/20919943



Change-Id: I63b3f5885831d75881611126e08cf8dfcfcd48dc
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>