Don't notify of changes to non-VFS state for inactive devices

There were three left over places where we could notifyChanged for
inactive devices:
(1) On Connected, we requestFocus() but ignored the status and updated
state anyway
(2) When browsing anything from the now playing scope we would always
notifyChanged for the node
(3) Cover art downloads for items in the now playing list would result
in notifyChanged calls even when inactive

Case (1) has been addressed by centralizing the state changes in
setActive() in a way thats safer and providers better testability in the
future. Case (2) was solved by checking the scope of a node before
updating anyone. Case (3) moved the notifications from the BrowseTree to
the state machine and piggy-backed off case (2)'s solution.

Tag: #compatibility
Bug: 154959439
Test: atest BluetoothInstrumentationTests, build/flash and test with
various target devices.

Change-Id: Id6967daaa057c4269186df3765ae760a7bb27ace