fix(fabric, textinput): implement selection properly (#2689)

## Summary:

This is part of a series of PRs where we are cherry-picking fixes from
#2117 to update our
Fabric implementation on macOS.

This is furthermore, a subset of commits from #2675 . This set
specifically implements the text selection APIs on TextInput for macOS,
along with another set of commits to reduce our diffs in
`RCTCopyBackedTextInput`

## Test Plan:

Tested the TextInput selection examples in RNTester. All seem to work
well.

---------

Co-authored-by: Shawn Dempsey <[email protected]>
Co-authored-by: Nick Lefever <[email protected]>

Author: 3 people

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

@@ -679,7 +679,11 @@ - (void)setTextAndSelection:(NSInteger)eventCount
     UITextRange *range = [_backedTextInputView textRangeFromPosition:startPosition toPosition:endPosition];
     [_backedTextInputView setSelectedTextRange:range notifyDelegate:NO];
   }
-#endif // [macOS]
+#else // [macOS
+  NSInteger startPosition = MIN(start, end);
+  NSInteger endPosition = MAX(start, end);
+  [_backedTextInputView setSelectedTextRange:NSMakeRange(startPosition, endPosition - startPosition) notifyDelegate:YES];
+#endif // macOS]
   _comingFromJS = NO;
 }
 
@@ -835,8 +839,8 @@ - (void)_updateState
                                                 toPosition:selectedTextRange.end];
   return AttributedString::Range{(int)start, (int)(end - start)};
 #else // [macOS
-  // [Fabric] Placeholder till we implement selection in Fabric
-  return AttributedString::Range({0, 1});
+  NSRange selectedTextRange = [_backedTextInputView selectedTextRange];
+  return AttributedString::Range{(int)selectedTextRange.location, (int)selectedTextRange.length};
 #endif // macOS]
 }
 
@@ -862,8 +866,12 @@ - (void)_setAttributedString:(NSAttributedString *)attributedString
   }
 #if !TARGET_OS_OSX // [macOS]
   UITextRange *selectedRange = _backedTextInputView.selectedTextRange;
+#else
+  NSRange selectedRange = [_backedTextInputView selectedTextRange];
+#endif // macOS]
   NSInteger oldTextLength = _backedTextInputView.attributedText.string.length;
   _backedTextInputView.attributedText = attributedString;
+#if !TARGET_OS_OSX // [macOS]
   // 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.
   // This is fixed by restoring the cursor position and scrolling to that position (iOS issue 652653).
@@ -882,7 +890,16 @@ - (void)_setAttributedString:(NSAttributedString *)attributedString
   [self _restoreTextSelection];
   [self _updateTypingAttributes];
   _lastStringStateWasUpdatedWith = attributedString;
-#endif // [macOS]
+#else // [macOS
+  if (selectedRange.length == 0) {
+    // Maintaining a cursor position relative to the end of the old text.
+    NSInteger start = selectedRange.location;
+    NSInteger offsetFromEnd = oldTextLength - start;
+    NSInteger newOffset = _backedTextInputView.attributedText.length - offsetFromEnd;
+    [_backedTextInputView setSelectedTextRange:NSMakeRange(newOffset, 0)
+                                      notifyDelegate:YES];
+  }
+#endif // macOS]
 }
 
 // Ensure that newly typed text will inherit any custom attributes. We follow the logic of RN Android, where attributes

packages/react-native/React/Fabric/Mounting/ComponentViews/TextInput/RCTTextInputUtils.h

@@ -18,13 +18,8 @@
 NS_ASSUME_NONNULL_BEGIN
 
 void RCTCopyBackedTextInput(
-#if !TARGET_OS_OSX // [macOS]
-    RCTUIView<RCTBackedTextInputViewProtocol> *fromTextInput,
-    RCTUIView<RCTBackedTextInputViewProtocol> *toTextInput
-#else // [macOS
-    RCTUITextView<RCTBackedTextInputViewProtocol> *fromTextInput,
-    RCTUITextView<RCTBackedTextInputViewProtocol> *toTextInput
-#endif // macOS]
+    RCTPlatformView<RCTBackedTextInputViewProtocol> *fromTextInput,
+    RCTPlatformView<RCTBackedTextInputViewProtocol> *toTextInput
 );
 
 #if !TARGET_OS_OSX // [macOS]

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

@@ -19,13 +19,8 @@
 }
 
 void RCTCopyBackedTextInput(
-#if !TARGET_OS_OSX // [macOS]
-    RCTUIView<RCTBackedTextInputViewProtocol> *fromTextInput,
-    RCTUIView<RCTBackedTextInputViewProtocol> *toTextInput
-#else // [macOS
-    RCTUITextView<RCTBackedTextInputViewProtocol> *fromTextInput,
-    RCTUITextView<RCTBackedTextInputViewProtocol> *toTextInput
-#endif // macOS]
+    RCTPlatformView<RCTBackedTextInputViewProtocol> *fromTextInput,
+    RCTPlatformView<RCTBackedTextInputViewProtocol> *toTextInput
 )
 {
   toTextInput.attributedText = RCTSanitizeAttributedString(fromTextInput.attributedText);