Dragging threshold on high DPI touch devices is too small

When using nested Flickables, wrong Flickable might be dragged due to some devices having very high DPI displays.

Qt uses the default value of 10 for startDragDistance stylehint for Android and iOS devices. This should probably be scaled with DPI.

Try running attached project on such device and try to flick vertically. Sometimes just horizontal flicking occurs when you don't intend to do it.

Setting startDragDistance higher reduces this.