[Enhancement] SwipeGestureRecognizer: Enable progressive tracking

[Elashi]

Summary

Allow user to handle progressive tracking in SwipeGestureRecognizer just like PanGestureRecognizer . This way I can show some animation during swipe operation before it is complete. Currently its command is only called upon completion.

API Changes

All what needs to be done to provide the requested feature is in the file SwipeGestureRecognizer. Just add one event OnDetectSwipe and trigger it in DetectSwipe. So simple change yet provides a lot.

Here is how the event is going to be used:

	var swipeGesture = new SwipeGestureRecognizer();
	swipeGesture.PanUpdated += OnDetectSwipe;
	GestureRecognizers.Add(swipeGesture);
}

private void OnDetectSwipe(object sender, DetectSwipeUpdatedEventArgs e)
{
	switch (e.StatusType)
	{
		case GestureStatus.Running:
			Content.TranslationX = _x + e.TotalX;
			// Content.TranslationY =_y + e.TotalY;
			break;
		case GestureStatus.Completed:
			break;
	}
}

Intended Use Case

I would like to create my own slide menu just like shell Flyout. During swipe, it feels as if you drag it from the side of the window to its final position.

[Elashi]

I wish I can derive from the class SwipeGestureRecognizer but it is sealed.
I tried to duplicate SwipeGestureRecognizer logic (and then customize it) by deriving directly from GestureRecognizer but this was not possible because GestureRecognizer's constructor is internal !

[Elashi]

If you accept this feature and no one is available to work on it, I will be glad to work on it.

[chrisgull]

I envision something similar, a Swiping event that reports current offset.
SwipingEventArgs would contain an XY offset, to track progress of the swipe.