QtBluetooth: extend error enums to handle missing permission errors

More and more permissions are required on Android (and iOS?) devices to perform different bluetooth-related actions.

Currently if the user does not provide the permissions, we usually report it as an UnknownError. Some classes also have a way to provide an error string, but in some cases we can only write some message to a debug log.

This can be very misleading to the users, so I suggest to extend the error enums with new error codes.

Here is the list of enums to check:

• QBluetoothDeviceDiscoveryAgent::Error
• QBluetoothLocalDevice::Error
• QBluetoothServer::Error
• QBluetoothServiceDiscoveryAgent::Error
• QLowEnergyController::Error