Add UVC support

This CL adds support for UVC GadgetFunction. UVC can be enabled/disabled
by setting the `ro.usb.uvc.enabled` property, and this CL makes sure
that the Settings app honors the property when showing USB functions to
the user.

Bug: 242344221
Test: Manually tested that the 'USB Webcam' option is present when the
      property is set, and removed when property is unset.
Change-Id: I5d1ff0a43d3c0c722bc9e03132a581da5c61bd76