[RCTTouchHandler] Add a small optimization to coordinate conversion (microsoft#1902)

Author: Saadnajmi

React/Base/RCTTouchHandler.m

@@ -229,11 +229,10 @@ - (void)_updateReactTouchAtIndex:(NSInteger)touchIndex
   NSEvent *nativeTouch = _nativeTouches[touchIndex];
   CGPoint location = nativeTouch.locationInWindow;
   RCTAssert(_cachedRootView, @"We were unable to find a root view for the touch");
-  CGPoint rootViewLocation = [_cachedRootView.window.contentView convertPoint:location toView:_cachedRootView];
+  CGPoint rootViewLocation = [_cachedRootView convertPoint:location fromView:nil];
+
   NSView *touchView = _touchViews[touchIndex];
   CGPoint touchViewLocation = [touchView convertPoint:location fromView:nil];
-  // JavaScript expects coordinates to have (0,0) at top left, unlike the macOS coordinate system
-  rootViewLocation.y = NSHeight([[_cachedRootView window] frame]) - rootViewLocation.y; 
 #endif // macOS]
 
   NSMutableDictionary *reactTouch = _reactTouches[touchIndex];