fix(iOS, Stack): center subview not visible/misaligned in header (#3489)

## Description

Fixes missing/misaligned center subview in header on iOS.

| before | after |
| --- | --- |
| <img width="1206" height="2622" alt="before"
src="https://github.com/user-attachments/assets/b38a076e-3d80-42f5-8bd3-12a649e856f1"
/> | <img width="1206" height="2622" alt="after"
src="https://github.com/user-attachments/assets/81ddc53d-f6a2-46fc-9a5b-566c42828408"
/> |

Fixes
#3482.

## Changes

- limit wrapping subviews and related logic to left and right subviews
only on iOS 26+ (previously, there was only an SDK macro, without
runtime check)

## Test code and steps to reproduce

Run `Test3446` to verify that pressables are still working. To test
center subview, use:

<details>
<summary>Test example</summary>

```tsx
import React from 'react';
import { View, Text } from 'react-native';
import { createNativeStackNavigator } from '@react-navigation/native-stack';
import Colors from '../shared/styling/Colors';

function MainScreen() {
  return <View style={{ backgroundColor: 'moccasin' }} />;
}

const Stack = createNativeStackNavigator();

export default function App() {
  return (
    <Stack.Navigator>
      <Stack.Screen
        name="Main"
        component={MainScreen}
        options={{
          headerLeft: () => <Text>a</Text>,
          headerTitle: () => <Text>b</Text>,
          headerRight: () => <Text>c</Text>,
          headerBackground: () => (
            <View
              style={{
                backgroundColor: Colors.PurpleLight80,
                width: '100%',
                height: 120,
              }}
            />
          ),
        }}
      />
    </Stack.Navigator>
  );
}
```
</details>

## Checklist

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

Author: kligarski

ios/RNSScreenStackHeaderSubview.mm

@@ -174,14 +174,17 @@ - (void)updateLayoutMetrics:(const react::LayoutMetrics &)layoutMetrics
         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};
+    if (self.needsAutoLayout) {
+      BOOL sizeHasChanged = _layoutMetrics.frame.size != layoutMetrics.frame.size;
+      _layoutMetrics = layoutMetrics;
+      if (sizeHasChanged) {
+        [self invalidateIntrinsicContentSize];
+      }
+    } else
 #endif // RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
+    {
+      self.bounds = CGRect{CGPointZero, frame.size};
+    }
     [self layoutNavigationBar];
   }
 }
@@ -206,56 +209,82 @@ - (void)reactSetFrame:(CGRect)frame
   // 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)];
+    if (self.needsAutoLayout) {
+      _lastReactFrameSize = frame.size;
+      [self invalidateIntrinsicContentSize];
+    } else
 #endif // RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
+    {
+      [super reactSetFrame:CGRectMake(0, 0, frame.size.width, frame.size.height)];
+    }
     [self layoutNavigationBar];
   }
 }
 
 #endif // RCT_NEW_ARCH_ENABLED
 
+#if RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
+
+// Starting from iOS 26, to center left and right subviews inside liquid glass backdrop,
+// we need to use auto layout. To make Yoga's layout work with auto layout, we pass information
+// from Yoga via `intrinsicContentSize`.
+- (BOOL)needsAutoLayout
+{
+  BOOL needsAutoLayout = NO;
+  if (@available(iOS 26.0, *)) {
+    needsAutoLayout = _type == RNSScreenStackHeaderSubviewTypeLeft || _type == RNSScreenStackHeaderSubviewTypeRight;
+  }
+  return needsAutoLayout;
+}
+
+#endif // RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
+
 #pragma mark - UIBarButtonItem specific
 
 - (UIBarButtonItem *)getUIBarButtonItem
 {
+  RCTAssert(
+      _type == RNSScreenStackHeaderSubviewTypeLeft || _type == RNSScreenStackHeaderSubviewTypeRight,
+      @"[RNScreens] Unexpected subview type.");
+
   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];
+    if (@available(iOS 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
 #endif // RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
+    {
+      _barButtonItem = [[UIBarButtonItem alloc] initWithCustomView:self];
+    }
     [self configureBarButtonItem];
   }
 
@@ -281,7 +310,7 @@ - (void)configureBarButtonItem
       [_barButtonItem setHidesSharedBackground:_hidesSharedBackground];
     }
   }
-#endif
+#endif // RNS_IPHONE_OS_VERSION_AVAILABLE(26_0)
 }
 
 - (void)setHidesSharedBackground:(BOOL)hidesSharedBackground