onTapCancel method
Called when there was an onTapDown event previously, but the onTapUp can no longer occur.
Usually this happens when the user starts a drag gesture, but could also occur for other reasons (e.g. another app coming to the foreground).
This event will be propagated to all components that has previously
received the onTapDown
event.
Implementation
@mustCallSuper
void onTapCancel(TapCancelEvent event) {
_tapCancelImpl(event);
}