Fix TextInput interfering with Japanese conversion

The bug happened anywhere we set a onChangeText event handler on TextInput, and rewrite the inflight text such as shown in
https://github.com/microsoft/react-native-macos/blob/main/packages/rn-tester/js/examples/TextInput/TextInputSharedExamples.js#L137

To fix we have to ignore changes to text if we have incomplete conversions.

Author: lyahdav

Libraries/Text/TextInput/RCTBackedTextInputViewProtocol.h

@@ -76,6 +76,7 @@ NS_ASSUME_NONNULL_BEGIN
 #endif // ]TODO(macOS GH#774)
 
 #if TARGET_OS_OSX // [TODO(macOS GH#774)
+- (BOOL)hasMarkedText;
 // UITextInput method for OSX
 - (CGSize)sizeThatFits:(CGSize)size;
 #endif // ]TODO(macOS GH#774)

Libraries/Text/TextInput/RCTBaseTextInputView.m

@@ -153,6 +153,12 @@ - (void)setAttributedText:(NSAttributedString *)attributedText
                                 range:NSMakeRange(0, attributedTextCopy.length)];
 
   textNeedsUpdate = ([self textOf:attributedTextCopy equals:backedTextInputViewTextCopy] == NO);
+#if TARGET_OS_OSX // [TODO(macOS GH#774)
+  // If we are in a language that uses conversion (e.g. Japanese), ignore updates if we have unconverted text.
+  if ([self.backedTextInputView hasMarkedText]) {
+    textNeedsUpdate = NO;
+  }
+#endif // ]TODO(macOS GH#774)
 
   if (eventLag == 0 && textNeedsUpdate) {
 #if !TARGET_OS_OSX // TODO(macOS GH#774)

Libraries/Text/TextInput/Singleline/RCTUITextField.m

@@ -127,6 +127,13 @@ - (void)_textDidChange
 #endif // ]TODO(macOS GH#774)
 }
 
+#if TARGET_OS_OSX // [TODO(macOS GH#774)
+- (BOOL)hasMarkedText
+{
+  return ((NSTextView *)self.currentEditor).hasMarkedText;
+}
+#endif // ]TODO(macOS GH#774)
+  
 #pragma mark - Accessibility
 
 #if !TARGET_OS_OSX // [TODO(macOS GH#774)