[IOS] No/disappearing Conversion Line when Typing CJK (Chinese, Japanese, Korean) Characters into TextInput (0.76.5)

Description

When typing CJK characters into TextInput, the conversion line (the line under the group of pre-formatted characters) disappears after typing the first character or doesn't appear at all.

https://github.com/user-attachments/assets/6afb4b71-cb77-406b-a768-8b5fbd775cf7

Steps to reproduce

1. npx create-expo-app@latest
2. In the home screen, add

import { useState } from 'react';
import { TextInput } from 'react-native';
...
  const [text, setText] = useState('')
  ...
    <TextInput value={text} onChangeText={setText} style={{ height: 50, width: '100%' }} />

3. Run the project with npm run ios
4. Type Japanese, Chinese, or Korean

React Native Version

0.76.5

Affected Platforms

Runtime - iOS

Output of npx react-native info

System:
  OS: macOS 15.1.1
  CPU: (8) arm64 Apple M2
  Memory: 164.45 MB / 8.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.5.1
    path: ~/.nvm/versions/node/v22.5.1/bin/node
  Yarn:
    version: 1.22.19
    path: /opt/homebrew/bin/yarn
  npm:
    version: 10.8.2
    path: ~/.nvm/versions/node/v22.5.1/bin/npm
  Watchman:
    version: 2024.12.02.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.15.2
    path: /usr/local/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.2
      - iOS 18.2
      - macOS 15.2
      - tvOS 18.2
      - visionOS 2.2
      - watchOS 11.2
  Android SDK: Not Found
IDEs:
  Android Studio: 2022.3 AI-223.8836.35.2231.10671973
  Xcode:
    version: 16.2/16C5032a
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 20.0.2
    path: /Users/personal/.jenv/shims/javac
  Ruby:
    version: 2.6.10
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react: Not Found
  react-native: Not Found
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found

Stacktrace or Logs

N/A

Reproducer

https://github.com/haruki-m/react-native-text-input-issue

Screenshots and Videos

No response

リンクされた react-native-text-input-issue の再現手順から始め、npm run ios で実行してから、日本語、中国語、韓国語の文字を入力している間の iOS TextInput の挙動を追跡します。issue では特定のソースファイルやテストは指定されていません。提供された再現手順で CJK のコンポジション中も変換行が表示されたままになることをもって完了とします。