Fix maintainVisibleContentPosition ignoring contentInset in Fabric ScrollView

The Fabric implementation of `_adjustForMaintainVisibleContentPosition` did
not account for `contentInset` when computing the autoscroll threshold
comparison or the scroll target position, unlike the Paper implementation
(`RCTScrollView.m`) which already handles this correctly.

When a non-zero `contentInset` is set on a scroll view, two bugs occurred:

1. The threshold comparison used raw `contentOffset` instead of the
   inset-adjusted value, causing autoscroll to fire incorrectly.
2. The autoscroll target was hardcoded to `0` instead of `-inset`, causing
   the scroll view to jump to the wrong position.

Fix: compute `bottomInset`/`leftInset` (respecting `isInverted`) and use
them to adjust both the threshold comparison and the `scrollToOffset` target,
matching the existing Paper logic in `RCTScrollView.m`.

No behavior change when `contentInset` is zero.

Author: enahum

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

@@ -1096,27 +1096,29 @@ - (void)_adjustForMaintainVisibleContentPosition
   if (horizontal) {
     CGFloat deltaX = _firstVisibleView.frame.origin.x - _prevFirstVisibleFrame.origin.x;
     if (ABS(deltaX) > 0.5) {
-      CGFloat x = _scrollView.contentOffset.x;
+      CGFloat leftInset = [self isInverted] ? _scrollView.contentInset.right : _scrollView.contentInset.left;
+      CGFloat x = _scrollView.contentOffset.x + leftInset;
       [self _forceDispatchNextScrollEvent];
       _scrollView.contentOffset = CGPointMake(_scrollView.contentOffset.x + deltaX, _scrollView.contentOffset.y);
       if (autoscrollThreshold) {
         // If the offset WAS within the threshold of the start, animate to the start.
         if (x <= autoscrollThreshold.value()) {
-          [self scrollToOffset:CGPointMake(0, _scrollView.contentOffset.y) animated:YES];
+          [self scrollToOffset:CGPointMake(-leftInset, _scrollView.contentOffset.y) animated:YES];
         }
       }
     }
   } else {
     CGRect newFrame = _firstVisibleView.frame;
     CGFloat deltaY = newFrame.origin.y - _prevFirstVisibleFrame.origin.y;
     if (ABS(deltaY) > 0.5) {
-      CGFloat y = _scrollView.contentOffset.y;
+      CGFloat bottomInset = [self isInverted] ? _scrollView.contentInset.top : _scrollView.contentInset.bottom;
+      CGFloat y = _scrollView.contentOffset.y + bottomInset;
       [self _forceDispatchNextScrollEvent];
       _scrollView.contentOffset = CGPointMake(_scrollView.contentOffset.x, _scrollView.contentOffset.y + deltaY);
       if (autoscrollThreshold) {
         // If the offset WAS within the threshold of the start, animate to the start.
         if (y <= autoscrollThreshold.value()) {
-          [self scrollToOffset:CGPointMake(_scrollView.contentOffset.x, 0) animated:YES];
+          [self scrollToOffset:CGPointMake(_scrollView.contentOffset.x, -bottomInset) animated:YES];
         }
       }
     }