[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

Start with the share_plus example project and reproduce the ShareParams case on iOS by choosing Gmail. Trace how the text and subject values from the code sample are passed into the share flow. Done means Gmail uses the supplied subject rather than the first sentence of the text, with the example or an appropriate test confirming the behavior.

Written by the indexing model from the issue text.