onLongPressCancel property Null safety
Called when a pointer that previously triggered onLongPressDown will not end up causing a long-press.
This triggers once the gesture loses the arena if onLongPressDown has previously been triggered.
If the gesture is deactivated due to postAcceptSlopTolerance having been exceeded, this callback will not be called, since the gesture will have already won the arena at that point.
- kPrimaryButton, the button this callback responds to.