FFMPEG Support in Qt6 Multimedia

This epic covers the work on supporting FFMEPG as aQt6 muiltimedia backend.

Background: Qt 6.2 Multimedia supports a number of graphics APIs such as macOS/iOS: AVFoundation, Linux: GStreamer, Windows: WMF, Android: Android Java API

Problem statement: All graphics API do not support the same lower level features such as seeking in the same way -> we get bug reports that we can’t fix and end up using a lot of extra time for multimedia features, and have inconsistent feature set

Proposed solution: 

Introduce support for a new multimedia backend, FFmpeg which supports a cross-platform API for the low-level features and can be used on all platforms: Linux, Windows, Mac, iOS and Android

Implication is that we need to integrate codecs into our release packages as FFMPEG includes codecs.