Camera: Add new hidden API for camera open/close callback

The hidden API is used by SystemUI process to adjust the system UI based
on when a certain camera is opened or closed.

Test: Manually observe callbacks in SystemUI when running camera CTS
Bug: 150540299
Change-Id: I04cae782d96f0e32be8ef588dcd328f84b32887a
Merged-In: I04cae782d96f0e32be8ef588dcd328f84b32887a