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

On Fabric, typed text in a TextInput renders too low when
lineHeight > fontSize — glyphs anchor to the bottom of the
attributed-string line box. Paper's facebook#38359 addressed this via
NSBaselineOffsetAttributeName, but the equivalent helper
RCTApplyBaselineOffset (already used by <Text> in RCTTextLayoutManager)
was never wired into the <TextInput> path.

Call RCTApplyBaselineOffset inside
RCTTextInputComponentView._setAttributedString: to add the baseline
offset before assigning the attributedString to the backed view. Widen
RCTNSAttributedStringFromAttributedString[Box] to return
NSMutableAttributedString * so the typed-text path avoids an extra
mutableCopy; the Value-mode path already built a mutable and returned
it typed as immutable, and OpaquePointer-mode now mutableCopy's
explicitly.

The helper alone is not enough: on each keystroke the attributedText
that round-trips UIKit → Fabric state → back drops
NSParagraphStyleAttributeName (UIKit's typingAttributes does not carry
the paragraph style, and _updateState stores the stripped attributedText
verbatim as an OpaquePointer). Without a paragraph style on the incoming
string, RCTApplyBaselineOffsetForRange reads maximumLineHeight == 0 and
returns early, so the offset is never applied to typed text.

Re-seed the paragraph style from defaultTextAttributes on any range
that lacks it (or carries a zero-lineHeight stub) before calling the
helper, so the offset is computed and applied for typed content too.

UITextView (multi-line) honors NSBaselineOffsetAttributeName for
rendered text; UITextField (single-line) does not — that path is
addressed in a separate commit.

Author: janicduplessis

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

@@ -575,8 +575,8 @@ - (void)setTextAndSelection:(NSInteger)eventCount
   }
   _comingFromJS = YES;
   if (value && ![value isEqualToString:_backedTextInputView.attributedText.string]) {
-    NSAttributedString *attributedString =
-        [[NSAttributedString alloc] initWithString:value attributes:_backedTextInputView.defaultTextAttributes];
+    NSMutableAttributedString *attributedString =
+        [[NSMutableAttributedString alloc] initWithString:value attributes:_backedTextInputView.defaultTextAttributes];
     [self _setAttributedString:attributedString];
     [self _updateState];
   }
@@ -766,8 +766,30 @@ - (void)_restoreTextSelectionAndIgnoreCaretChange:(BOOL)ignore
   [_backedTextInputView setSelectedTextRange:range notifyDelegate:YES];
 }
 
-- (void)_setAttributedString:(NSAttributedString *)attributedString
+- (void)_setAttributedString:(NSMutableAttributedString *)attributedString
 {
+  // When the user types, UIKit's typingAttributes drop NSParagraphStyleAttributeName, so the
+  // attributedText round-tripping back through state lacks the paragraph style that
+  // RCTApplyBaselineOffset needs. Re-seed paragraph style from defaultTextAttributes on ranges
+  // that are missing it or carry a zero-lineHeight stub, so the helper can compute the offset.
+  NSParagraphStyle *defaultParagraphStyle =
+      _backedTextInputView.defaultTextAttributes[NSParagraphStyleAttributeName];
+  if (defaultParagraphStyle && attributedString.length > 0) {
+    [attributedString
+        enumerateAttribute:NSParagraphStyleAttributeName
+                   inRange:NSMakeRange(0, attributedString.length)
+                   options:0
+                usingBlock:^(NSParagraphStyle *style, NSRange range, __unused BOOL *stop) {
+                  if (!style || style.maximumLineHeight == 0) {
+                    [attributedString addAttribute:NSParagraphStyleAttributeName
+                                             value:defaultParagraphStyle
+                                             range:range];
+                  }
+                }];
+  }
+
+  RCTApplyBaselineOffset(attributedString);
+
   if ([self _textOf:attributedString equals:_backedTextInputView.attributedText]) {
     return;
   }

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

@@ -28,10 +28,10 @@ NSMutableDictionary<NSAttributedStringKey, id> *RCTNSTextAttributesFromTextAttri
 /*
  * Conversions amond `NSAttributedString`, `AttributedString` and `AttributedStringBox`.
  */
-NSAttributedString *RCTNSAttributedStringFromAttributedString(
+NSMutableAttributedString *RCTNSAttributedStringFromAttributedString(
     const facebook::react::AttributedString &attributedString);
 
-NSAttributedString *RCTNSAttributedStringFromAttributedStringBox(
+NSMutableAttributedString *RCTNSAttributedStringFromAttributedStringBox(
     const facebook::react::AttributedStringBox &attributedStringBox);
 
 facebook::react::AttributedStringBox RCTAttributedStringBoxFromNSAttributedString(

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

@@ -405,7 +405,7 @@ void RCTApplyBaselineOffset(NSMutableAttributedString *attributedText)
   return nsAttributedStringFragment;
 }
 
-NSAttributedString *RCTNSAttributedStringFromAttributedString(const AttributedString &attributedString)
+NSMutableAttributedString *RCTNSAttributedStringFromAttributedString(const AttributedString &attributedString)
 {
   static UIImage *placeholderImage;
   static dispatch_once_t onceToken;
@@ -428,13 +428,13 @@ void RCTApplyBaselineOffset(NSMutableAttributedString *attributedText)
   return nsAttributedString;
 }
 
-NSAttributedString *RCTNSAttributedStringFromAttributedStringBox(const AttributedStringBox &attributedStringBox)
+NSMutableAttributedString *RCTNSAttributedStringFromAttributedStringBox(const AttributedStringBox &attributedStringBox)
 {
   switch (attributedStringBox.getMode()) {
     case AttributedStringBox::Mode::Value:
       return RCTNSAttributedStringFromAttributedString(attributedStringBox.getValue());
     case AttributedStringBox::Mode::OpaquePointer:
-      return (NSAttributedString *)unwrapManagedObject(attributedStringBox.getOpaquePointer());
+      return [(NSAttributedString *)unwrapManagedObject(attributedStringBox.getOpaquePointer()) mutableCopy];
   }
 }