fix(macos): Break the corebluetooth loop when manager turned off

[dmtrKovalenko]

closes https://github.com/deviceplug/btleplug/issues/387

In Core Bluetooth when the device is locked or suspended and it is not applicable for background Bluetooth access the manager will create an event for state change and after will change the manager state to powerOff. Currently, it is not tracked at all which leads to the forever stuck unresolved futures while the connection to peripheral is still held.

An additional problem I faced that there is no way to manually kill the event loop of the corebluetooth from outside so the CoreBluetoothInternal::drop is never called because it is always living in the stalled thread.

In this change, I added an API to access the manager state and exited the event loop when if the manager turned off.

[qdot]

Ok, well, should've merged this before the corebluetooth API change. Patch looks fine but I need to go back and see what the conflicts are and if this is still valid given the event loop changes made during the API change.