Register Qt Multimedia DShow back-end in ROT for debugging

When Qt Multimedia is using the DirectShow back-end on Windows, it would be very useful if it registered the filter graph with the ROT so that the graph can be viewed and debugged with GraphEdit / GraphStudio/Next.

See https://docs.microsoft.com/en-us/windows/win32/directshow/loading-a-graph-from-an-external-process for details. Registering the graph allows connections to it to be made from other processes.

I'll leave how to enable/disable this as an open question, some of my ideas (brainstorming) are:

• Maybe one of the QMediaPlayer flags – but then it would only apply when using QMediaPlayer.
• A command line option (parsed by QApplication)
• A global enable/disable method somewhere
• A QApplication attribute.
• A QMediaObject flag / property
• A QMediaContent flag / property
• An environment variable (meh)
• Just always have it enabled.

I'm a fan of a command line option for some reason, but it really doesn't matter to me.