Have AvrcpControllerService own the active device

This code moves the active device management from functions around a
static objects on the state machine to a functions from the
AvrcpControllerService.

AvrcpControllerService now orchestrates the active device. A device will
become active when:
1. It connects and no other device is connected
2. When you browse that device
3. When you play an item from that device

AvrcpControllerService notifies state machines of their active state
with a new message that goes on the handler. State machines then update
the BluetoothMediaBrowserService accordingly. When there is no active
device set, AvrcpControllerService will clear the
BluetoothMediaBrowserService status. When a new/different device is set,
AvrcpControllerService will send a pause to the previous device.

New tests have been added to prove state machine behavior.

Tag: #stability
Bug: 180416295
Bug: 180416562
Bug: 181374758
Bug: 181374973
Test: atest BluetoothInstrumentationTests
Change-Id: I251498bec049fc4cdfd4e657558649c5cfd3dd6c