Add the AVRCP Target Service (1/2)

The AVRCP Target Service is started by Bluetooth Adapter like a normal
service instead of being started by A2DP like the old service. All it
does is initializes the player list and helps communicate data between
the Media Framework and the Native Interface.

Bug: 68854188
Test: Compiles and local test with service enabled
Change-Id: Ifb26f0fa3fac37686924bd6835e1d346ebf68bf1