Consider adding Raw* widgets to the widget catalog

### Page URL

https://docs.flutter.dev/ui/widgets

### Describe the problem

From discussions online, we've been adding more basic components to the widgets layer in preparation for decoupling, refactoring some features out of design for better use in developing your own design language or styles.

Note: Not all of them are specifically prepended with `Raw*', like `RawMenuAnchor` some are mixins and more, like `ToggleableStateMixn` (now in widgets) and `Expansible`.

cc @victorsanni @justinmc