[PTS-Bot]:Implementation to support accessing Browsing folder and Media Player selection commands

Added file MediaPlayerBrowserService.kt and MediaPlayer.kt

This is a service which extends "MediaBrowserService" with MediaSession and initial implementation to support browsing folders.
With registration to Media buttons callback which responds to PTT commands(Tried with Play/Pause..).

Moved AudioTrack from A2DP.kt to Utils.kt
All Player operations are performed in MediaPlayer.kt

Reference for older CL: 2253995

Added 21 AVRCP test cases for review

Test: atest pts-bot:AVRCP -v

Change-Id: Icee2a268faa3cbac4cd0001d09baec82eeb01f9d