NEW_API: Rework CameraSound into MediaActionSound, and unhide it.

MediaActionSound is a helper class for applications that use the
camera, or include camera-like behavior such as taking
screenshots. This class helps applications match the sound-playing
behavior of the Camera.takePicture, MediaRecorder.start, and
MediaRecorder.stop methods.

This is useful for applications that don't use the above methods, but
still logically capture images or video, such as the panorama capture
feature and the video effects in the platform camera application.

Bug: 5029099
Change-Id: I829f6e2941f167f91f9cb506215b7232cb054958