feat(iOS): use system context menu in iOS(for secure paste)

[kexuejin]

Based on the PR template you provided, here's the Pull Request content prepared for your system context menu feature modification:

Description

This PR modifies the Flutter Quill editor's context menu building logic to prioritize QuillSystemContextMenu when config.useSystemContextMenuItems is set to true . This change enables iOS secure paste functionality and improves user experience with native system context menus.

New behavior: When useSystemContextMenuItems is true and the platform supports it, the editor uses QuillSystemContextMenu.quillEditor() to display native system menus; if not supported, it falls back to the original menu building logic.

Motivation: To fully utilize iOS system-provided secure paste functionality and native user experience.

Related Issues

• Related to iOS secure paste functionality improvements

Type of Change

• ✨ Feature: New functionality without breaking existing features.
• 🛠️ Bug fix: Resolves an issue without altering current behavior.
• 🧹 Refactor: Code reorganization, no behavior change.
• ❌ Breaking: Alters existing functionality and requires updates.
• 🧪 Tests: New or modified tests
• 📝 Documentation: Updates or additions to documentation.
• 🗑️ Chore: Routine tasks, or maintenance.
• ✅ Build configuration change: Build/configuration changes.

[kexuejin]

Since Flutter's SystemContextMenu only supports text in the clipboard, if there is an image in the clipboard, SystemContextMenu will not provide the Paste Menu.

[EchoEllet]

Since Flutter's SystemContextMenu only supports text in the clipboard, if there is an image in the clipboard, SystemContextMenu will not provide the Paste Menu.

We do have quill_native_bridge to address this issue; however, it currently does not support Windows and does not support Linux well (especially in sandboxed environments in case of Flatpak).