A pointer that has triggered a long-press with a primary button has stopped contacting the screen.
This is equivalent to (and is called immediately after) onLongPressEnd. The only difference between the two is that this callback does not contain details of the state of the pointer when it stopped contacting the screen.
- kPrimaryButton, the button this callback responds to.
- LongPressGestureRecognizer.onLongPressUp, which exposes this callback at the gesture layer.
final GestureLongPressUpCallback? onLongPressUp;