longpressup support

Runtime/gestures/long_press.cs

             base(deadline: Constants.kLongPressTimeout, debugOwner: debugOwner, kind: kind) {
         }
 
+        bool _longPressAccepted = false;
+
+        public GestureLongPressUpCallback onLongPressUp;
+
+            this._longPressAccepted = true;
+
             if (this.onLongPress != null) {
                 this.invokeCallback<object>("onLongPress", () => {
                     this.onLongPress();
 
         protected override void handlePrimaryPointer(PointerEvent evt) {
             if (evt is PointerUpEvent) {
-                this.resolve(GestureDisposition.rejected);
+                if (this._longPressAccepted && this.onLongPressUp != null) {
+                    this._longPressAccepted = false;
+                    this.invokeCallback<object>("onLongPressUp", () => {
+                        this.onLongPressUp();
+                        return null;
+                    });
+                }
+                else {
+                    this.resolve(GestureDisposition.rejected);
+                }
+            }
+            else if (evt is PointerDownEvent || evt is PointerCancelEvent) {
+                this._longPressAccepted = false;
             }
         }
 

Runtime/widgets/gesture_detector.cs

                 gestures[typeof(LongPressGestureRecognizer)] =
                     new GestureRecognizerFactoryWithHandlers<LongPressGestureRecognizer>(
                         () => new LongPressGestureRecognizer(debugOwner: this),
-                        instance => { instance.onLongPress = this.onLongPress; }
+                        instance => {
+                            instance.onLongPress = this.onLongPress;
+                            instance.onLongPressUp = this.onLongPressUp;
+                        }
                     );
             }