Phonon MMF: enabling full screen when rendering on external display causes video to disappear

Environment:
Device: N8
Qt: either qt-s60-public/4.6 commit 38df4707, or qt-s60-public/4.7 commit 1c1094a4

Steps to reproduce:
1. Launch qmediaplayer
2. Start video playback
[Video + UI is rendered on device]
3. Plug in HDMI cable
[Video disappears from device; UI remains on device; video is rendered full-screen on external display]
4. Enable full-screen mode by selecting from menu

Expected behaviour:
Full-screen option should be checked and disabled when routed to the external display

Observed behaviour:
Both internal and external displays go completely black

Comments:

• We need to check whether the backend receives a notification from the MMF (e.g. via the MVideoPlayerUtilityObserver::MvpuoEvent callback) when video is routed to an external display. If not, it may be necessary to subscribe to another native API to receive this notification.
• Once the backend knows that it is routed to the external display, the best it can do is to ignore full-screen switch notifications. Because the fullscreen status is held within the Phonon::VideoWidget, and is not propagated to the backend directly (only via a geometry change on the backend widget), the backend can neither update the fullscreen status, nor prevent it from being modified by the client application.