Triggered when a pointer moves into a position within this widget without buttons pressed.
Usually this is only fired for pointers which report their location when not down (e.g. mouse pointers). Certain devices also fire this event on single taps in accessibility mode.
This callback is not triggered by the movement of the widget.
The time that this callback is triggered is during the callback of a pointer event, which is always between frames.
final PointerHoverEventListener? onHover;