AVFoundation: Add QVideoWindowControl support

This adds the capability to render videos directly to native
window surfaces when using the AVFoundation plugin.  This adds limited
support for displaying videos from QML on iOS.  These videos are
displayed in a CALayer above the QQuickWindow, so it will not be
possible to render any QtQuick items on top of a video using the
QVideoWindowControl to provide video.

[ChangeLog][QtMultimedia][iOS] Add limited support for playing videos in
QtQuick on iOS (Videos are played on top of scene with limited transform
support).

Change-Id: I80381d9a07b45b6fa1959678166e6da0004f8c19
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>