Trigger OS's UI to pick/exclude targets for capture

[clearlysid]

All major OSes have a native way of selecting what all screens to capture for a given session. It would be nice to be able to trigger the picker from scap and receive it's output as Targets which we can then pass to the capture_engine.

More reading:

1. https://learn.microsoft.com/en-us/uwp/api/windows.graphics.capture.graphicscapturepicker?view=winrt-22621
2. https://developer.apple.com/documentation/screencapturekit/sccontentsharingpicker
3. https://github.com/electron/electron/issues/39043

Not a personal prio for me at the moment, but happy to help out someone if they want to work on this.