Chore: Move spellchecker service to extensions

[CatHood0]

Description

Since SimpleSpellCheckerService is a custom implementation that is not needed by default, was moved to Flutter Quill Extensions and can be used such as SuperClipboard implementation:

FlutterQuillExtensions.useSpellCheckerService('<your_language>');

And was fixed some issue with some missing characters while typing (this is for languages such as portuguese, deutsch, italian, etc)

• [ ] ✨ New feature: Adds new functionality without breaking existing features.
• [ ] 🛠️ Bug fix: Resolves an issue without altering current behavior.
• [x] 🧹 Code refactor: Code restructuring that does not affect behavior.
• [ ] ❌ Breaking change: Alters existing functionality and requires updates.
• [ ] 🧪 Tests: Adds new tests or modifies existing tests.
• [ ] 📝 Documentation: Updates or additions to documentation.
• [ ] 🗑️ Chore: Routine tasks, or maintenance.
• [ ] ✅ Build configuration change: Changes to build or deploy processes.

Suggestions

Please, after update the version of the main repo, also update it into flutter_quill_extensions to avoid conflicts since the new version change the names of the classes and methods.