TextInput is unstable for Korean. (iOS only)

[toy0605]

Please provide all the information requested. Issues that do not follow this format are likely to stall.

Description

Hi.
I found the issue on iOS devices.
I'm typing with Korean on TextInput. but font size changes madly or flickering during typing.
It's fine for english. It only has issue for Korean or mixing english and korean.

It causes from two ways.

1. Font family is not assigned.
2. Font family is Korean font.(NotoSansKR or Apple SD Gothic Neo) It looks good this way. but If add props like value and event handler(onChangeText) for changing value, it makes unstable, too.

It only works very well functionally. appearance is so bad.

That issue very annoying to me.

React Native version:

System:
    OS: macOS 10.15.5
    CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
    Memory: 738.23 MB / 32.00 GB
    Shell: 5.7.1 - /bin/zsh
  Binaries:
    Node: 14.0.0 - /usr/local/bin/node
    Yarn: 1.22.4 - /usr/local/bin/yarn
    npm: 6.14.4 - /usr/local/bin/npm
    Watchman: 4.9.0 - /usr/local/bin/watchman
  Managers:
    CocoaPods: 1.9.2 - /usr/local/bin/pod
  SDKs:
    iOS SDK:
      Platforms: iOS 13.5, DriverKit 19.0, macOS 10.15, tvOS 13.4, watchOS 6.2
    Android SDK: Not Found
  IDEs:
    Android Studio: 3.6 AI-192.7142.36.36.6392135
    Xcode: 11.5/11E608c - /usr/bin/xcodebuild
  Languages:
    Java: 1.8.0_252 - /usr/bin/javac
    Python: 2.7.16 - /usr/bin/python
  npmPackages:
    @react-native-community/cli: Not Found
    react: 16.11.0 => 16.11.0
    react-native: 0.62.2 => 0.62.2
  npmGlobalPackages:
    *react-native*: Not Found

Steps To Reproduce

The issue for TextInput only. Not Text component.

1. Font family is none.
2. Font family is Korean font. but using props(value and onChangeText)

and typing Korean text.

Expected Results

I just want it looks stable.

Snack, code example, screenshot, or link to a repository:

<TextInput style={{width: "100%", backgroundColor: "#eeeeee", fontSize: 14}}/>

<TextInput style={{width: "100%", backgroundColor: "#eeeeee", fontFamily: "NotoSansKR-Regular", fontSize: 14}}
value={this.state.textValue}
onChangeText={(text) => this.setState({textValue: text})}/>

[toy0605]

If multiline is true, it works very well strangely.

[javascripter]

This happens with Japanese too.

When there is some English character before Japanese, the font size stays stable. Otherwise it causes significant layout instability.

[firevitality]

Chinese without English too.

[mengheangrat]

It's RN issue. You can use this patch.
https://github.com/ifsnow/react-native-cjk-textinput-patch#readme

[chrisglein]

Fixed by #28805

[wbw20]

I tested this fix on #8c392ff and it seems to work well for me, but it seems to be broken on 0.63.0.