onSecondaryLongPressUp property Null safety
A pointer that has triggered a long-press with a secondary button has stopped contacting the screen.
This is equivalent to (and is called immediately after) onSecondaryLongPressEnd. 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.
final GestureLongPressUpCallback? onSecondaryLongPressUp;