Coding agreements in DevTools

We fully follow Effective Dart and some items of Style guide for Flutter repo:

Order of getters and setters

When an object owns and exposes a (listenable) value, more complicated than just public field we declare the related class members always in the same order, in compliance with Flutter repo style guide:

1. Public getter
2. Private field
3. Public setter (when needed)

Naming for typedefs and function variables

Follow Flutter repo naming rules for typedefs and function variables.