[Bug]: Subject message is ignored(First sentence of text is taken instead)

### Platform

iOS 26.6

### Plugin

share_plus

### Version

13.3.0

### Flutter SDK

3.44.6

### Steps to reproduce

Share message from code sample and choose Gmail

### Code Sample

```dart
ShareParams(
text: "You're invited to XXX — join and get something.\nhttps.xxxx.com"
subject: "You're invited to XXX",
);
```

### Logs

```shell
-
```

### Flutter Doctor

```shell
[✓] Flutter (Channel stable, 3.44.6, on macOS 26.5.1 25F80 darwin-arm64 (Rosetta), locale en-GB) [6.0s]
• Flutter version 3.44.6 on channel stable at /Users/xxxxx/fvm/versions/3.44.6
• Upstream repository https://github.com/flutter/flutter.git
• Framework revision ee80f08bbf (8 weeks ago), 2026-07-08 15:02:06 -0700
• Engine revision 83675ed276
• Dart version 3.12.2
• DevTools version 2.57.0
• Feature flags: enable-web, enable-linux-desktop, enable-macos-desktop, enable-windows-desktop,
enable-android, enable-ios, cli-animations, enable-native-assets, enable-swift-package-manager,
omit-legacy-version-file, enable-lldb-debugging, enable-uiscene-migration
```

### Checklist before submitting a bug

- [x] I searched issues in this repository and couldn't find such bug/problem
- [x] I Google'd a solution and I couldn't find it
- [x] I searched on StackOverflow for a solution and I couldn't find it
- [x] I read the README.md file of the plugin
- [x] I'm using the latest version of the plugin
- [x] All dependencies are up to date with `flutter pub upgrade`
- [x] I did a `flutter clean`
- [x] I tried running the example project

share_plus のサンプルプロジェクトから始め、Gmail を選択して iOS 上で ShareParams のケースを再現します。コードサンプルの text と subject の値が共有フローにどのように渡されるかを追跡します。Gmail が text の最初の文ではなく、指定された subject を使用し、サンプルまたは適切なテストでその動作が確認できれば完了です。

索引モデルが issue の本文から書いたものです。