Dart and Flutter Language support
**What is language?**
Dart is a programming language that can be compiled to run on mobile, desktop and web.
Flutter is a UI framework that works on top of Dart and runs natively on any of the above platforms.

**Which platform does the language support?**

- [x] Linux
- [x] MacOS
- [x] Windows

**Any suggest vim plugins for this language?**
[vim-flutter](https://github.com/thosakwe/vim-flutter)
[dart-vim-plugin](https://github.com/dart-lang/dart-vim-plugin)
[coc-flutter](https://github.com/iamcco/coc-flutter)

**Additional context**
Add any other context or screenshots about the feature request here.
