[Web] Composing Japanese letters disappear when shifting converting area

### Steps to reproduce

1. launch an app with `TextField` on web platform
2. type some letters in Hiragana, Japanese.
3. before committing (by hitting the Enter key), hit the Space key to convert them to Kanji.
4. press Shift and hit the left arrow key twice
5. composing Hiragana letters disappear

### Expected results

The composing Hiragana letters don't disappear, and the composing area would shift respecting the arrow key hit.

### Actual results

All the composing Hiragana letters disappear.

### Code sample

<details open><summary>Code sample</summary>

```dart
void main() => runApp(const MainApp());

class MainApp extends StatelessWidget {
  const MainApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Padding(
          padding: const EdgeInsets.all(32),
          child: Container(
            width: double.infinity,
            color: Colors.white,
            child: const Padding(
              padding: EdgeInsets.all(16),
              child: TextField(),
            ),
          ),
        ),
      ),
    );
  }
}
```

</details>


### Screenshots or Video

<details open>
<summary>Screenshots / Video demonstration</summary>

https://github.com/user-attachments/assets/50f5c200-8e3d-4ff1-9457-3c08224d8be6


</details>


### Logs

<details open><summary>Logs</summary>

```console
[Paste your logs here]
```

</details>


### Flutter Doctor output

<details open><summary>Doctor output</summary>

```console
$ fvm flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.24.5, on macOS 14.3.1 23D60 darwin-arm64, locale ja-JP)
[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
[✓] Xcode - develop for iOS and macOS (Xcode 15.4)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2022.3)
[✓] Android Studio (version 2022.2)
[✓] VS Code (version 1.94.2)
[✓] VS Code (version 1.61.2)
[✓] Connected device (4 available)
[✓] Network resources

• No issues found!
```

</details>


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[Web] Composing Japanese letters disappear when shifting converting area #159671

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[Web] Composing Japanese letters disappear when shifting converting area #159671

Description

Steps to reproduce

Expected results

Actual results

Code sample

Screenshots or Video

Logs

Flutter Doctor output

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions