fix(ios): center TextInput text when lineHeight > fontSize on Fabric

Summary:
Ports the Paper-only fix from facebook#38359 to the Fabric (new arch) path.
When `lineHeight` is set larger than the font's intrinsic line height,
UIKit anchors glyphs to the bottom of the attributed-string line box,
making typed text visually sit too low while the placeholder (which
uses a different rendering path) stays correctly centered.

The `RCTApplyBaselineOffset` helper that Paper's fix relies on already
ships in Fabric (`RCTAttributedTextUtils.mm`) and is invoked for
`<Text>` rendering in `RCTTextLayoutManager`, but was never wired into
the `<TextInput>` path. This calls it inside
`RCTTextInputComponentView._setAttributedString:`.

This regression against Paper is tracked in facebook#39145. It has been
reported repeatedly for the new architecture (see comments referring
back to facebook#38359).

Changelog:
[IOS] [FIXED] - Center typed TextInput text when lineHeight > fontSize
on the new architecture.

Test Plan:
Added an RN Tester example ("Single-line lineHeight baseline" under
TextInput examples) that renders a single-line TextInput at a range
of lineHeight values with a fixed fontSize. Before this change,
typing into any of these inputs shows text bottom-anchored inside
the line box while the placeholder is centered. After this change,
typed text centers alongside the placeholder.

Related: facebook#38359, facebook#39145

Author: janicduplessis

packages/react-native/React/Fabric/Mounting/ComponentViews/TextInput/RCTTextInputComponentView.mm

@@ -768,6 +768,23 @@ - (void)_restoreTextSelectionAndIgnoreCaretChange:(BOOL)ignore
 
 - (void)_setAttributedString:(NSAttributedString *)attributedString
 {
+  // When `lineHeight` is greater than the font's intrinsic line height,
+  // UIKit anchors glyphs to the bottom of the attributed-string line box,
+  // causing typed text to render visually too low while the placeholder
+  // (which uses a different rendering path) stays centered.
+  //
+  // The same fix was applied to the Paper (old arch) renderer in #38359
+  // via `RCTBaseTextInputShadowView.postprocessAttributedText:`. Fabric
+  // already ships the equivalent `RCTApplyBaselineOffset` helper (used by
+  // `<Text>` in `RCTTextLayoutManager`) but never invoked it on the
+  // `<TextInput>` path. Apply it here so typed text is centered within
+  // the expanded line box.
+  //
+  // Tracked by https://github.com/facebook/react-native/issues/39145.
+  NSMutableAttributedString *mutableAttributedString = [attributedString mutableCopy];
+  RCTApplyBaselineOffset(mutableAttributedString);
+  attributedString = mutableAttributedString;
+
   if ([self _textOf:attributedString equals:_backedTextInputView.attributedText]) {
     return;
   }

packages/rn-tester/js/examples/TextInput/TextInputSharedExamples.js

@@ -1188,6 +1188,38 @@ module.exports = [
     name: 'textStyles',
     render: () => <TextStylesExample />,
   },
+  {
+    title: 'Single-line lineHeight baseline',
+    name: 'lineHeightBaseline',
+    description:
+      'Regression repro for https://github.com/facebook/react-native/issues/39145. ' +
+      'When lineHeight > fontSize on a single-line TextInput, typed text should ' +
+      'stay vertically centered. Placeholder centering is already correct; the ' +
+      'bug is that typed glyphs anchor to the bottom of the attributed-string ' +
+      'line box, appearing visually too low.',
+    render: function (): React.Node {
+      return (
+        <View>
+          {[20, 24, 32, 48].map(lineHeight => (
+            <WithLabel
+              key={lineHeight}
+              label={`fontSize: 16, lineHeight: ${lineHeight}`}>
+              <ExampleTextInput
+                placeholder="placeholder stays centered"
+                style={{
+                  fontSize: 16,
+                  lineHeight,
+                  borderColor: '#ccc',
+                  borderWidth: 1,
+                  padding: 8,
+                }}
+              />
+            </WithLabel>
+          ))}
+        </View>
+      );
+    },
+  },
   {
     title: 'showSoftInputOnFocus',
     render: function (): React.Node {