[FEATURE] - Add separators for more symbols

[alefragnani]

More symbols could have their own separators.

• [x] Class
• [x] Interface
• [x] Enum
• [x] Namespace

Please, suggest/vote 😬

Here you can find all kinds of symbols supported by VS Code, and that each language extension must provides/adapt: https://code.visualstudio.com/api/references/vscode-api#SymbolKind

[JCKodel]

I've opened the https://github.com/alefragnani/vscode-separators/issues/7 regarding Dart constructions (it works only on methods or constructors).

Basically, all "class-like" (class, interface, enum, mixin, extension), all methods (get/set accessors, methods, constructors).

If each group could have its own color would be amazing.

[JCKodel]

Please, add support for Namespace because of this: https://github.com/Dart-Code/Dart-Code/issues/2945#issuecomment-724846211