Add multi-client support in camera2

Add support for multiple clients to access the same camera using
camera2 api. This is initial set of changes and includes all the new
API changes as well as implementation of opening the camera in shared
mode, new open callbacks, newly added characteristics and creating
shared sesion.

After the merge of these initial changes, it will be followed by
another set of changes which will include implementation of
startStreaming and stopStreaming APIs and the capability for multiple
clients to stream the camera images.

Flag: com.android.internal.camera.flags.camera_multi_client
Bug:265196098
API-Coverage-Bug: 377371012
Test: Tested that a java and native client are able to open the camera
at the same time and get the required callbacks and they are able to get
the shared session configuration using newly added characteristics.
Tested the clientaccessprioritieschanged callback occur appropriately
when new client connects/disconnects.

Change-Id: I4cd3babf538b065d635c99c695718d8f52883afc