apply method
Applies this operation to the current list.
Modifies current in place and returns the effective operation
(e.g. populated with captured state like removed index).
Implementation
@override
OverlayOp apply(List<InteractiveOverlayImage> list) {
final old = list.findByKeyOrNull(key);
if (old == null) return this;
final next = _withCorner(old, corner, to);
list.updateByKey(key, next);
return this;
}