SystemServer: unbind prior to setting state

When transitioning to stateOff, the caller of `waitForState` are
notified before the unbind is completed.
The caller will expect that when reaching OFF, everything is OFF.

By calling unbindAndFinish prior to setting the state, we reduce the
probability of this scenario

Test: atest ServiceBluetoothRoboTests
Test: atest ServiceBluetoothTests
Test: atest CtsBluetoothTestCases
Test: basically any code that toggles Bluetooth off and on
Flag: Exempt this targets flakiness and is checked with abtd
Bug: 361850050
Change-Id: If3a5e6e358e295a2f77619d5f1c82c69c950a6e2