MediatranscodingService: Create MediaTranscodingService.

"adb shell dumpsys -l | grep media" shows media.transcoding service.

This CL only adds the skelton to start the service and hook up with the
libmediatranscoding librarie now. But it does not do anything yet. The
implementation will be added in the next few Cls.

Bug:145233472
Test: Build and run.

Change-Id: I09021b811e5bd935735b0b936c55639496799ae1