Ensure the connected device indicator disappears if bluetooth is turned

off.

This requires exposing BluetoothController as a protected variable so
that CarStatusBar can pass it to the ConnectedDeviceSignalController.
The latter controller is then aware of when bluetooth is turned off and
can appropriately hide the indicators.

Test: Manually tested
Bug: 31711141
Change-Id: I7657b6d1210eb31f162fe358e34f480f88fc3268