DragEndCallback typedef Null safety
Signature for when the draggable is dropped.
The velocity and offset at which the pointer was moving when the draggable
was dropped is available in the DraggableDetails. Also included in the
details
is whether the draggable's DragTarget accepted it.
Used by Draggable.onDragEnd.
Implementation
typedef DragEndCallback = void Function(DraggableDetails details);