Preserve TextInput returnKeyType when changing multiline

RCTCopyBackedTextInput copies the keyboard traits over to the replacement
backing view when a TextInput switches between single-line and multiline,
but omits returnKeyType. The prop itself is unchanged across the
transition, so the prop diff does not re-run the setter and the new view
keeps its default Return key.

Copy returnKeyType alongside keyboardType, and add a regression test next
to the existing tintColor one.

Author: jamfromouterspace

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

@@ -43,6 +43,7 @@ void RCTCopyBackedTextInput(
   toTextInput.scrollEnabled = fromTextInput.scrollEnabled;
   toTextInput.secureTextEntry = fromTextInput.secureTextEntry;
   toTextInput.keyboardType = fromTextInput.keyboardType;
+  toTextInput.returnKeyType = fromTextInput.returnKeyType;
   toTextInput.textContentType = fromTextInput.textContentType;
   toTextInput.smartInsertDeleteType = fromTextInput.smartInsertDeleteType;
   toTextInput.passwordRules = fromTextInput.passwordRules;

packages/react-native/React/Tests/Text/RCTTextInputUtilsTest.mm

@@ -26,4 +26,15 @@ - (void)testCopyBackedTextInputPreservesTintColor
   XCTAssertEqualObjects(destination.tintColor, UIColor.redColor);
 }
 
+- (void)testCopyBackedTextInputPreservesReturnKeyType
+{
+  RCTUITextField *source = [RCTUITextField new];
+  RCTUITextView *destination = [RCTUITextView new];
+  source.returnKeyType = UIReturnKeyDone;
+
+  RCTCopyBackedTextInput(source, destination);
+
+  XCTAssertEqual(destination.returnKeyType, UIReturnKeyDone);
+}
+
 @end