[platform_views] Fix duplicated touch event pass down to flutter view from platform view.

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews.mm

@@ -353,6 +353,21 @@ - (void)blockGesture {
   _delayingRecognizer.get().state = UIGestureRecognizerStateEnded;
 }
 
+// We want the intercepting view to consume the touches and not pass the touches up to the parent
+// view. Make the touch event method not call super will not pass the touches up to the parent view.
+// Hence we overide the touch event methods and do nothing.
+- (void)touchesBegan:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event {
+}
+
+- (void)touchesMoved:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event {
+}
+
+- (void)touchesCancelled:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event {
+}
+
+- (void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event {
+}
+
 @end
 
 @implementation DelayingGestureRecognizer {
@@ -395,19 +410,24 @@ @implementation ForwardingGestureRecognizer {
   // So this is safe as when FlutterView is deallocated the reference to ForwardingGestureRecognizer
   // will go away.
   UIView* _flutterView;
+  // Counting the pointers that has started in one touch sequence.
+  NSInteger _currentTouchPointersCount;
 }
 
 - (instancetype)initWithTarget:(id)target flutterView:(UIView*)flutterView {
   self = [super initWithTarget:target action:nil];
   if (self) {
     self.delegate = self;
     _flutterView = flutterView;
+    _currentTouchPointersCount = 0;
   }
   return self;
 }
 
 - (void)touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event {
   [_flutterView touchesBegan:touches withEvent:event];
+  _currentTouchPointersCount += touches.count;
+  [_flutterView touchesBegan:touches withEvent:event];
 }
 
 - (void)touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event {
@@ -416,11 +436,19 @@ - (void)touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event {
 
 - (void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event {
   [_flutterView touchesEnded:touches withEvent:event];
-  self.state = UIGestureRecognizerStateFailed;
+  _currentTouchPointersCount -= touches.count;
+  // Touches in one touch sequence are sent to the touchesEnded method separately if different
+  // fingers stop touching the screen at different time. So one touchesEnded method triggering does
+  // not necessarially mean the touch sequence has ended. We Only set the state to
+  // UIGestureRecognizerStateFailed when all the touches in the current touch sequence is ended.
+  if (_currentTouchPointersCount == 0) {
+    self.state = UIGestureRecognizerStateFailed;
+  }
 }
 
 - (void)touchesCancelled:(NSSet*)touches withEvent:(UIEvent*)event {
   [_flutterView touchesCancelled:touches withEvent:event];
+  _currentTouchPointersCount = 0;
   self.state = UIGestureRecognizerStateFailed;
 }