Derive multiline TextInput state from props (#59218)

Summary:
Pull Request resolved: #59218

Use `TextInputProps::multiline` as the source of truth for multiline checks instead of inferring it from the backed UIKit class. This keeps responder offset and selection restoration logic aligned with the declarative props.

Changelog: [Internal]

Reviewed By: Abbondanzo

Differential Revision: D126285220

fbshipit-source-id: 42274a5f57189257ee27e21de2940c3df28b6205

Author: cipolleschi

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

@@ -180,7 +180,8 @@ - (void)reactUpdateResponderOffsetForScrollView:(RCTScrollViewComponentView *)sc
   } else {
     // Focus on text selection frame
     focusRect = selection.rect;
-    BOOL isMultiline = [_backedTextInputView isKindOfClass:[UITextView class]];
+    BOOL isMultiline = _props ? static_cast<const TextInputProps &>(*_props).multiline
+                              : [_backedTextInputView isKindOfClass:[UITextView class]];
     if (!isMultiline) {
       focusRect.size.height += kSingleLineKeyboardBottomOffset;
     }
@@ -859,7 +860,8 @@ - (void)_setAttributedString:(NSAttributedString *)attributedString
   // A single-line input that is not being edited has no cursor to keep: UIKit places one when editing begins.
   // Restoring it anyway makes UIKit scroll the field editor to it when the text doesn't fit, and the editor keeps
   // that offset after the text fits again, so text typed later in this view (also after recycling) is drawn too high.
-  BOOL isMultiline = [_backedTextInputView isKindOfClass:[UITextView class]];
+  BOOL isMultiline = _props ? static_cast<const TextInputProps &>(*_props).multiline
+                            : [_backedTextInputView isKindOfClass:[UITextView class]];
   if (isMultiline || _backedTextInputView.isFirstResponder) {
     // Updating the UITextView attributedText, for example changing the lineHeight, the color or adding
     // a new paragraph with \n, causes the cursor to move to the end of the Text and scroll.