fix(iOS 26, Stack): center view inside bar button item (#3449)

## Description

Fixes alignment of custom view inside bar button item on iOS 26.

> [!NOTE]
>
> Please note that this will also change positioning of bar button items
with `hidesSharedBackground: true` on iOS 26.

| before | after |
| --- | --- |
| <video
src="https://github.com/user-attachments/assets/d188be5c-48bf-4dee-97e2-599eac487af0"
/> | <video
src="https://github.com/user-attachments/assets/82d5ca33-8ef2-40bb-8d4e-030b0b53054c"
/> |

Closes
#2990.

### Explanation

Starting from iOS 26, custom view inside `UIBarButtonItem` is stretched
to at least 36 width. This causes our `RNSScreenStackHeaderSubview` to
stretch if its width is smaller than 36, leaving subviews in the same
origin (for one subview, it's usually `(0,0)`; that's why it is aligned
to the left, visible in "before" recording).

In order to mitigate this, we add `wrapperView` which will be stretched
by UIKit to required minimum size. `RNSScreenStackHeaderSubview` will be
centered inside of it. Additional constraints and properties needed to
be added to make sure that `wrapperView` is not stretched to all
available space in `UINavigationBar` (this would happen in `headerRight`
if we used only `wrapperView.width >= RNSScreenStackHeaderSubview.width`
constraint):

- `wrapperView.width == RNSScreenStackHeaderSubview.width` - makes sure
that wrapper matches content. By using lower priority than default, we
allow UIKit to "take over" with its minimum width, while maintaining
"fit-content"/"content hugging" behavior,
- `[self setContentHuggingPriority:UILayoutPriorityRequired
forAxis:UILayoutConstraintAxisHorizontal]` - prevents stretching to all
available width in `UINavigationBar`.

`RNSScreenStackHeaderSubview` needs to use `intrinsicContentSize` in
order to bridge auto-layout centering and frame size from Yoga.

## Changes

- on iOS 26, add wrapper view between `UIBarButtonItem` and
`RNSScreenStackHeaderSubview`
- center `RNSScreenStackHeaderSubview` inside `wrapperView` while
maintaining correct sizing via auto layout
- use `intrinsicContentSize` to bridge between auto-layout and frames
calculated by Yoga
- fix frame passed to shadow tree (now, `RNSScreenStackHeaderSubview`
can have non-zero offset (which was not the case previously); without
change to `self.bounds`, this offset would be accounted for 2 times when
using `[self convertRect:frame toView:ancestorView]`)

## Test code and steps to reproduce

Run `Test3446`.

## Checklist

- [x] Included code example that can be used to test this change
- [x] Ensured that CI passes

Author: kligarski

ios/RNSScreenStackHeaderSubview.mm

@@ -20,10 +20,13 @@
 #endif // RCT_NEW_ARCH_ENABLED
 
 @implementation RNSScreenStackHeaderSubview {
-#ifdef RCT_NEW_ARCH_ENABLED
+#if RCT_NEW_ARCH_ENABLED
   react::RNSScreenStackHeaderSubviewShadowNode::ConcreteState::Shared _state;
   CGRect _lastScheduledFrame;
-#endif
+#endif // RCT_NEW_ARCH_ENABLED
+#if !RCT_NEW_ARCH_ENABLED && RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
+  CGSize _lastReactFrameSize;
+#endif // !RCT_NEW_ARCH_ENABLED && RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
   // TODO: Refactor this, so that we don't keep reference here at all.
   // Currently this likely creates retain cycle between subview & the bar button item.
   UIBarButtonItem *_barButtonItem;
@@ -88,7 +91,7 @@ - (void)updateShadowStateInContextOfAncestorView:(nullable UIView *)ancestorView
 
 - (void)updateShadowStateInContextOfAncestorView:(nullable UIView *)ancestorView
 {
-  [self updateShadowStateInContextOfAncestorView:ancestorView withFrame:self.frame];
+  [self updateShadowStateInContextOfAncestorView:ancestorView withFrame:self.bounds];
 }
 
 - (void)updateShadowStateWithFrame:(CGRect)frame
@@ -170,7 +173,15 @@ - (void)updateLayoutMetrics:(const react::LayoutMetrics &)layoutMetrics
         NSStringFromCGRect(frame),
         self);
   } else {
+#if RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
+    BOOL sizeHasChanged = _layoutMetrics.frame.size != layoutMetrics.frame.size;
+    _layoutMetrics = layoutMetrics;
+    if (sizeHasChanged) {
+      [self invalidateIntrinsicContentSize];
+    }
+#else // RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
     self.bounds = CGRect{CGPointZero, frame.size};
+#endif // RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
     [self layoutNavigationBar];
   }
 }
@@ -194,23 +205,74 @@ - (void)reactSetFrame:(CGRect)frame
   // Block any attempt to set coordinates on RNSScreenStackHeaderSubview. This
   // makes UINavigationBar the only one to control the position of header content.
   if (!CGSizeEqualToSize(frame.size, self.frame.size)) {
+#if RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
+    _lastReactFrameSize = frame.size;
+    [self invalidateIntrinsicContentSize];
+#else // RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
     [super reactSetFrame:CGRectMake(0, 0, frame.size.width, frame.size.height)];
+#endif // RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
     [self layoutNavigationBar];
   }
 }
+
 #endif // RCT_NEW_ARCH_ENABLED
 
 #pragma mark - UIBarButtonItem specific
 
 - (UIBarButtonItem *)getUIBarButtonItem
 {
   if (_barButtonItem == nil) {
+#if RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
+    // Starting from iOS 26, UIBarButtonItem's customView is streched to have at least 36 width.
+    // Stretching RNSScreenStackHeaderSubview means that its subviews are aligned to left instead
+    // of the center. To mitigate this, we add a wrapper view that will center
+    // RNSScreenStackHeaderSubview inside of itself.
+    UIView *wrapperView = [UIView new];
+    wrapperView.translatesAutoresizingMaskIntoConstraints = NO;
+
+    self.translatesAutoresizingMaskIntoConstraints = NO;
+    [wrapperView addSubview:self];
+
+    [self.centerXAnchor constraintEqualToAnchor:wrapperView.centerXAnchor].active = YES;
+    [self.centerYAnchor constraintEqualToAnchor:wrapperView.centerYAnchor].active = YES;
+
+    // To prevent UIKit from stretching subviews to all available width, we need to:
+    // 1. Set width of wrapperView to match RNSScreenStackHeaderSubview BUT when
+    //    RNSScreenStackHeaderSubview's width is smaller that minimal required 36 width, it breaks
+    //    UIKit's constraint. That's why we need to lower the priority of the constraint.
+    NSLayoutConstraint *widthEqual = [wrapperView.widthAnchor constraintEqualToAnchor:self.widthAnchor];
+    widthEqual.priority = UILayoutPriorityDefaultHigh;
+    widthEqual.active = YES;
+
+    NSLayoutConstraint *heightEqual = [wrapperView.heightAnchor constraintEqualToAnchor:self.heightAnchor];
+    heightEqual.priority = UILayoutPriorityDefaultHigh;
+    heightEqual.active = YES;
+
+    // 2. Set content hugging priority for RNSScreenStackHeaderSubview.
+    [self setContentHuggingPriority:UILayoutPriorityRequired forAxis:UILayoutConstraintAxisHorizontal];
+    [self setContentHuggingPriority:UILayoutPriorityRequired forAxis:UILayoutConstraintAxisVertical];
+
+    _barButtonItem = [[UIBarButtonItem alloc] initWithCustomView:wrapperView];
+#else // RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
     _barButtonItem = [[UIBarButtonItem alloc] initWithCustomView:self];
+#endif // RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
     [self configureBarButtonItem];
   }
+
   return _barButtonItem;
 }
 
+#if RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
+- (CGSize)intrinsicContentSize
+{
+#if RCT_NEW_ARCH_ENABLED
+  return RCTCGSizeFromSize(_layoutMetrics.frame.size);
+#else // RCT_NEW_ARCH_ENABLED
+  return _lastReactFrameSize;
+#endif // RCT_NEW_ARCH_ENABLED
+}
+#endif // RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
+
 - (void)configureBarButtonItem
 {
 #if RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)