Try recognizing implicitly unthrottled windows

Follow up to QTBUG-99951

It would be very handy if we could trigger the fallback to the non-vsync-driven animations when recognizing that presentation is going too fast, meaning that there is no vsync-based throttling even though the application did request it (as that is the default in Qt).

What "too fast" is is of course not quite clear: we could start with something simple, e.g. if the elapsed time (on the gui thread) between syncs is less than half of the vsync interval for multiple frames.

This will not affect render thread animations (the NNNAnimator QML types). Those cannot be helped if the vsync is not there, they will advance too fast. But if we could get normal animations functions sanely out of the box even when vsync is not working, that would already be a big step forward.