fix(ios): align text to the right by default in RTL (#57634)

Summary:
On the new architecture, `<Text>` without an explicit `textAlign` behaves differently across platforms when the layout direction is RTL:

- **Android**: text aligns to the right (follows the layout direction).
- **iOS**: text stays left-aligned (ignores the layout direction).

This is a regression from the old architecture, where both platforms left text alone when `textAlign` was unset. The new arch changed Android's default, and the two platforms are now inconsistent.

This PR makes iOS match the current Android (new arch) behavior: without an explicit `textAlign`, text follows the layout direction and aligns to the right in RTL. On iOS, `Natural` alignment now resolves to `Right` under RTL.

### Open question

I aligned iOS to Android's new default, but I'm not sure it's the right call (my guts feeling think that is the right thing to do, tho). The old-arch behavior (do nothing when `textAlign` is unset) may be what's actually expected, in which case the fix should go the other way: revert Android to leave text untouched and keep iOS as-is. Happy to flip the direction if reviewers prefer that.

## Changelog:

[IOS] [FIXED] - Align text to the right by default in RTL when `textAlign` is not set, matching Android

Pull Request resolved: #57634

Test Plan:
Edit `RNTesterAppShared.js`, press the button, reload the app - comment / uncomment `Text` `textAlign` style:

```js
/**
 * flow
 * format
 */

import {
  I18nManager,
  SafeAreaView,
  StyleSheet,
  Text,
  TouchableOpacity,
  View,
} from 'react-native';

I18nManager.allowRTL(true);
I18nManager.swapLeftAndRightInRTL(true);

export default function App(): React.Node {
  const isRTL = I18nManager.isRTL;

  return (
    <View style={styles.wrapper}>
      <SafeAreaView style={styles.content}>
        <Text style={styles.info}>I18nManager.isRTL: {String(isRTL)}</Text>

        <TouchableOpacity
          onPress={() => I18nManager.forceRTL(!isRTL)}
          style={styles.button}>
          <Text style={styles.buttonText}>Toggle RTL + reload manually</Text>
        </TouchableOpacity>

        <View style={styles.row}>
          <View style={[styles.box, {backgroundColor: '#FF6B6B'}]}>
            <Text style={styles.boxText}>1</Text>
          </View>
          <View style={[styles.box, {backgroundColor: '#4ECDC4'}]}>
            <Text style={styles.boxText}>2</Text>
          </View>
          <View style={[styles.box, {backgroundColor: '#45B7D1'}]}>
            <Text style={styles.boxText}>3</Text>
          </View>
        </View>

        <Text
        // style={{textAlign: 'left'}} // COMMENT / UNCOMMENT THIS
        >
          Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do
          eiusmod tempor incididunt ut labore et dolore magna aliqua.
        </Text>
      </SafeAreaView>
    </View>
  );
}

const styles = StyleSheet.create({
  wrapper: {
    backgroundColor: 'white',
    flex: 1,
  },
  content: {
    gap: 20,
    marginHorizontal: 20,
  },
  info: {
    fontSize: 18,
    fontWeight: 'bold',
  },
  button: {
    backgroundColor: '#007AFF',
    padding: 15,
    borderRadius: 8,
  },
  buttonText: {
    color: 'white',
    textAlign: 'center',
    fontWeight: '600',
  },
  row: {
    flexDirection: 'row',
    justifyContent: 'space-around',
  },
  box: {
    width: 60,
    height: 60,
    alignItems: 'center',
    justifyContent: 'center',
    borderRadius: 8,
  },
  boxText: {
    color: 'white',
    fontSize: 18,
    fontWeight: 'bold',
  },
});
```

**Old architecture (baseline):**

| Android | iOS |
| --- | --- |
| <img width="503" height="935" alt="android - old arch" src="https://github.com/user-attachments/assets/6051bfac-ae5e-454d-94e3-b632e9062b55" /> | <img width="568" height="1084" alt="ios - old arch" src="https://github.com/user-attachments/assets/8c216962-ccf1-40d7-bd81-227331aaf288" /> |

**New architecture (before this PR, iOS diverges):**

| Android | iOS |
| --- | --- |
| <img width="503" height="935" alt="android - new arch" src="https://github.com/user-attachments/assets/35fcc60e-e172-42b8-af54-6360d4425757" /> | <img width="568" height="1084" alt="ios - new arch - not fixed" src="https://github.com/user-attachments/assets/2b558f16-94b5-4f8a-adb6-90f777e69fa0" /> |

**New architecture (after this PR, iOS fixed):**

| Android | iOS |
| --- | --- |
| <img width="503" height="935" alt="android - new arch" src="https://github.com/user-attachments/assets/35fcc60e-e172-42b8-af54-6360d4425757" /> | <img width="568" height="1084" alt="ios - new arch - fixed" src="https://github.com/user-attachments/assets/9467f96c-2ef1-46fa-8209-4f8e45b14c21" /> |

Reviewed By: javache

Differential Revision: D113244783

Pulled By: Abbondanzo

fbshipit-source-id: 75edbc2a2a2e1567de12c83375272672cc2683e9

Author: zoontek

packages/react-native/ReactCommon/react/renderer/textlayoutmanager/platform/ios/react/renderer/textlayoutmanager/RCTAttributedTextUtils.mm

@@ -18,10 +18,11 @@
 
 using namespace facebook::react;
 
-inline static TextAlignment RCTResolveTextAlignment(TextAlignment textAlignment, LayoutDirection layoutDirection)
+inline static TextAlignment RCTResolveTextAlignment(TextAlignment textAlignment, bool isRTL)
 {
-  const bool isRTL = layoutDirection == LayoutDirection::RightToLeft;
   switch (textAlignment) {
+    case TextAlignment::Natural:
+      return isRTL ? TextAlignment::Right : TextAlignment::Left;
     case TextAlignment::Start:
       return isRTL ? TextAlignment::Right : TextAlignment::Left;
     case TextAlignment::End:
@@ -212,10 +213,10 @@ inline static CGFloat RCTEffectiveFontSizeMultiplierFromTextAttributes(const Tex
   // Paragraph Style
   NSMutableParagraphStyle *paragraphStyle = [NSMutableParagraphStyle new];
   BOOL isParagraphStyleUsed = NO;
-  if (textAttributes.alignment.has_value()) {
-    TextAlignment textAlignment = RCTResolveTextAlignment(
-        textAttributes.alignment.value_or(TextAlignment::Natural),
-        textAttributes.layoutDirection.value_or(LayoutDirection::LeftToRight));
+  const bool isRTL = textAttributes.layoutDirection == LayoutDirection::RightToLeft;
+  if (textAttributes.alignment.has_value() || isRTL) {
+    TextAlignment textAlignment =
+        RCTResolveTextAlignment(textAttributes.alignment.value_or(TextAlignment::Natural), isRTL);
 
     paragraphStyle.alignment = RCTNSTextAlignmentFromTextAlignment(textAlignment);
     isParagraphStyleUsed = YES;