SystemUI: Fix shutter sound

* When shutter sound for camera is forced on as required in some states,
  (config_camera_sound_forced, set via mcc/mnc), we also want to
  (or should) play it when a screenshot is taken from the preview
  instead of an actual picture
* This change is loosely based on
  https://android-review.googlesource.com/c/platform/frameworks/base/+/1517742/
  but uses publicly available APIs

Testing:
- Set config_camera_sound_forced to true and push a build to device
- Turn down all stream volumes to muted
- Take screenshot of any normal screen
  -> No sound played
- Open camera, take screenshot
  -> Sound played
- Turn up volume and repeat the screenshots
  -> Sound played in all cases

Change-Id: Iacbb577c64f73b79cdfae7fb0487fc6a34ffe41c