virtual-input-device/native: Enable PHYSICAL_VIRTUAL device mode
IBus needs to distinguish whether key events are generated by physical keyboards or On-screen keyboard. CLUTTER_INPUT_MODE_PHYSICAL_VIRTUAL flag is applied to MetaInputDeviceNative so that ClutterInputDevice applies CLUTTER_EVENT_FLAG_OSK flag to ClutterEvent with OSK. META_TYPE_INPUT_DEVICE_NATIVE.