chore: deprecate flutter_quill/extensions.dart

[EchoEllet]

Description

Deprecate usages of extensions.dart to indicate that it's for internal usage only. Add flutter_quill_internal.dart as a replacement.

I have seen that some users are using the extensions.dart directly in their project which is a file for flutter_quill_extensions only and contains internal APIs that will change and update for the extensions package without any notice, which introduce breaking changes, users are often don't see the file itself from source and use it directly. Adding a comment is not clear enough. The flutter_quill_internal makes sure to make it more clear that it's for internal usage only.

Should increase the minimum version of flutter_quill_extensions by flutter_quill.

Type of Change

• [ ] ✨ New feature: Adds new functionality without breaking existing features.
• [ ] 🛠️ Bug fix: Resolves an issue without altering current behavior.
• [ ] 🧹 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.
• [x] 📝 Documentation: Updates or additions to documentation.
• [x] 🗑️ Chore: Routine tasks, or maintenance.
• [ ] ✅ Build configuration change: Changes to build or deploy processes.

Suggestions

For now, avoid introducing APIs as part of the public API, make it more clear it's for internal usage only using docs comment and internal annotation.

[EchoEllet]

It seems that we're using the extensions.dart that exposes the internal API to flutter_quill_extensions inside of flutter_quill. The new name should avoid confusion and be more specific.

Which is:

import 'package:flutter_quill/flutter_quill_internal.dart

Can also be:

import 'package:flutter_quill/internal.dart