AVRCP Controller play while browsing

Update state machine to handle asynchronous controller data while
browsing.  Specifically, resolve issues where long running browser fetch
commands are in progress when a track changes or user presses the play
button.

Bug: 131087752
Test: atest AvrcpControllerStateMachineTest
Change-Id: I046b41af5d03cfe7f5f068a9f8615a15fb25e9b2
(cherry picked from commit 3949ea6c)