DynamicCamera: Add new hidden APIs in CameraManager and new permission for injection camera

- Add new hidden APIs: injectCamera() and stopInjection() in
CameraManager.
- Add a new permission: android.permission.CAMERA_INJECT_EXTERNAL_CAMERA
to allow injecting the external camera to switch the internal camera.
- Add a new CameraInjectionSession class with stopInjection function,
which is called back by CameraInjectionCallback.onInjectionSucceeded(),
then the lifetime of CameraInjectionSession is what determines when
injection is active.

Bug: 181395010
Test: Verified camera manager use cases function as expected; no denials
Change-Id: I0b218dc6a55c7827e2446502b7a22382c6fe9f3e