Function simulate_drag 

pub fn simulate_drag<T: Clone + PartialEq + 'static>(
    dom: &mut VirtualDom,
    payload: T,
    from: Option<ZoneId>,
    path: &[Point],
) -> Option<ZoneId>

One whole pointer drag: pick payload up (from from), glide through path, release at its last point, re-rendering between steps so zone reactions run just as they would live. Returns the receiving zone, or None when the drag cancelled. Needs a mounted DragSimProbe<T>; an empty path releases at the pickup point.