fix(ios): center TextInput text, placeholder, and caret when lineHeight > fontSize

On iOS, when a `TextInput` has `lineHeight > fontSize`, UIKit misrenders three
surfaces:

1. Typed text — glyphs anchor to the bottom of the attributed-string line box
   instead of centering within it.
2. Placeholder — inherits the paragraph style from `defaultTextAttributes` and
   sits low.
3. Single-line caret — sized to the full paragraph line-box height rather than
   the font height, visibly taller than the glyph.

The fix splits two ways depending on which UIKit draw path is involved:

- UITextView (multi-line) and the UILabel-based placeholder paths honor
  `NSBaselineOffsetAttributeName`. Computing
  `(maxLineHeight - font.lineHeight) / 2` and applying it as a baseline offset
  re-centers the glyph in the line box.

- UITextField's UIFieldEditor draw path does not honor
  `NSBaselineOffsetAttributeName` for typed text, and the caret rect is sized
  from the same paragraph-style line box. For single-line inputs we instead
  zero the paragraph-style line height for the value passed to UIKit.
  UITextField then renders at the font's natural line height and its built-in
  vertical centering positions the glyph in the bounds; the caret rect shrinks
  to match. `defaultTextAttributes` keeps the unmodified paragraphStyle so the
  placeholder path still sees the real lineHeight, and Yoga's frame-height
  measurement is unaffected.

The typed-text fix lives in `RCTTextInputComponentView._setAttributedString:`
so it runs against text round-tripped through UIKit's `typingAttributes` (which
drops `NSParagraphStyleAttributeName`); we re-seed paragraph style from
`defaultTextAttributes` before applying the offset / strip. The placeholder
fixes are local to `_placeholderTextAttributes` in each backing view since both
backing views are shared between Paper and Fabric.

## Changelog

[IOS] [FIXED] - Center typed TextInput text, placeholder, and single-line caret when `lineHeight > fontSize`.

## Test Plan

RN Tester → **TextInput → lineHeight baseline** renders one single-line and
one multi-line `TextInput` with `fontSize: 16, lineHeight: 32`. Before:
placeholder sits low, typed glyphs anchor to the bottom of the line box,
single-line caret overshoots the glyph. After: placeholder and typed text
render vertically centered; single-line caret matches the glyph height.

Author: janicduplessis

packages/react-native/Libraries/Text/TextInput/Multiline/RCTUITextView.mm

@@ -364,6 +364,13 @@ - (void)_updatePlaceholder
     [textAttributes setValue:defaultPlaceholderFont() forKey:NSFontAttributeName];
   }
 
+  // The placeholder UILabel honors NSBaselineOffsetAttributeName.
+  NSParagraphStyle *paragraphStyle = textAttributes[NSParagraphStyleAttributeName];
+  UIFont *font = textAttributes[NSFontAttributeName];
+  if (paragraphStyle && font && paragraphStyle.maximumLineHeight > font.lineHeight) {
+    textAttributes[NSBaselineOffsetAttributeName] = @((paragraphStyle.maximumLineHeight - font.lineHeight) / 2.0);
+  }
+
   return textAttributes;
 }
 

packages/react-native/Libraries/Text/TextInput/Singleline/RCTUITextField.mm

@@ -169,6 +169,13 @@ - (void)setDisableKeyboardShortcuts:(BOOL)disableKeyboardShortcuts
     [textAttributes removeObjectForKey:NSForegroundColorAttributeName];
   }
 
+  // UILabel-based draw path used by `attributedPlaceholder` honors NSBaselineOffsetAttributeName.
+  NSParagraphStyle *paragraphStyle = textAttributes[NSParagraphStyleAttributeName];
+  UIFont *font = textAttributes[NSFontAttributeName];
+  if (paragraphStyle && font && paragraphStyle.maximumLineHeight > font.lineHeight) {
+    textAttributes[NSBaselineOffsetAttributeName] = @((paragraphStyle.maximumLineHeight - font.lineHeight) / 2.0);
+  }
+
   return textAttributes;
 }
 

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

@@ -768,6 +768,31 @@ - (void)_restoreTextSelectionAndIgnoreCaretChange:(BOOL)ignore
 
 - (void)_setAttributedString:(NSAttributedString *)attributedString
 {
+  // When `lineHeight > font.lineHeight`, UIKit's draw paths anchor glyphs to the bottom of the
+  // paragraph line box. UITextView honors NSBaselineOffsetAttributeName to re-center; UITextField
+  // does not, so we zero the paragraph line height instead and let UITextField's built-in
+  // vertical centering position the glyph (this also shrinks the otherwise-too-tall caret).
+  NSDictionary<NSAttributedStringKey, id> *defaults = _backedTextInputView.defaultTextAttributes;
+  NSParagraphStyle *paragraphStyle = defaults[NSParagraphStyleAttributeName];
+  UIFont *font = defaults[NSFontAttributeName];
+  if (attributedString.length > 0 && paragraphStyle && font &&
+      paragraphStyle.maximumLineHeight > font.lineHeight) {
+    NSMutableAttributedString *mutableString = [attributedString mutableCopy];
+    NSRange fullRange = NSMakeRange(0, mutableString.length);
+    if ([_backedTextInputView isKindOfClass:[RCTUITextView class]]) {
+      [mutableString addAttribute:NSParagraphStyleAttributeName value:paragraphStyle range:fullRange];
+      [mutableString addAttribute:NSBaselineOffsetAttributeName
+                            value:@((paragraphStyle.maximumLineHeight - font.lineHeight) / 2.0)
+                            range:fullRange];
+    } else {
+      NSMutableParagraphStyle *stripped = [paragraphStyle mutableCopy];
+      stripped.minimumLineHeight = 0;
+      stripped.maximumLineHeight = 0;
+      [mutableString addAttribute:NSParagraphStyleAttributeName value:stripped range:fullRange];
+    }
+    attributedString = mutableString;
+  }
+
   if ([self _textOf:attributedString equals:_backedTextInputView.attributedText]) {
     return;
   }