Fix momentum begin dispatch order (facebook#47578)

Summary:

In `RCTScrollView`, it was possible that `onMomentumScrollBegin` gets queued after `onMomentumScrollEnd` because the event would dispatch after calling `setContentOffset`. As a result, the ScrollView JS gets stuck in an "animating" state and jest runners did not bother scrolling further.

## Changelog:
[iOS][Fixed] - Momentum begin events now queue before momentum end events on scroll views

Differential Revision: D65846878

packages/react-native/React/Fabric/Mounting/ComponentViews/ScrollView/RCTScrollViewComponentView.mm

@@ -897,14 +897,18 @@ - (void)scrollToOffset:(CGPoint)offset animated:(BOOL)animated
 
   [self _forceDispatchNextScrollEvent];
 
+  // Notify of momentum scroll begin before setting content offset or events can fire out of order and scrollview gets
+  // stuck in "animating" state
+  if (animated && _eventEmitter) {
+    static_cast<const ScrollViewEventEmitter &>(*_eventEmitter).onMomentumScrollBegin([self _scrollViewMetrics]);
+  }
+
   [_scrollView setContentOffset:offset animated:animated];
 
   if (!animated) {
     // When not animated, the expected workflow in ``scrollViewDidEndScrollingAnimation`` after scrolling is not going
     // to get triggered. We will need to manually execute here.
     [self _handleFinishedScrolling:_scrollView];
-  } else if (_eventEmitter) {
-    static_cast<const ScrollViewEventEmitter &>(*_eventEmitter).onMomentumScrollBegin([self _scrollViewMetrics]);
   }
 }
 

packages/react-native/React/Views/ScrollView/RCTScrollView.m

@@ -599,10 +599,12 @@ - (void)scrollToOffset:(CGPoint)offset animated:(BOOL)animated
       y = fmin(y, CGRectGetMaxY(maxRect));
       offset = CGPointMake(x, y);
     }
-    [_scrollView setContentOffset:offset animated:animated];
+    // Notify of momentum scroll begin before setting content offset or events can fire out of order and scrollview gets
+    // stuck in "animating" state
     if (animated) {
       [self sendScrollEventWithName:@"onMomentumScrollBegin" scrollView:_scrollView userData:nil];
     }
+    [_scrollView setContentOffset:offset animated:animated];
   }
 }
 
@@ -624,10 +626,12 @@ - (void)scrollToEnd:(BOOL)animated
   if (!CGPointEqualToPoint(_scrollView.contentOffset, offset)) {
     // Ensure at least one scroll event will fire
     _allowNextScrollNoMatterWhat = YES;
-    [_scrollView setContentOffset:offset animated:animated];
+    // Notify of momentum scroll begin before setting content offset or events can fire out of order and scrollview gets
+    // stuck in "animating" state
     if (animated) {
       [self sendScrollEventWithName:@"onMomentumScrollBegin" scrollView:_scrollView userData:nil];
     }
+    [_scrollView setContentOffset:offset animated:animated];
   }
 }