Add AVRCP Controller Unit tests

Add unit tests to verify key functionality of the AVRCP Controller
service.  The tests of the state machine indirectly verify the
functionality of the other supporting classes.

Bug: 120673113
Test: atest com.android.bluetooth.avrcpcontroller
Change-Id: I3b230eae075e2ce541d94305a4c981c274dc0c57
(cherry picked from commit a533aad8)