Consider adding Raw* widgets to the widget catalog

[Piinks]

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 RawMenuAnchorsome are mixins and more, likeToggleableStateMixn(now in widgets) andExpansible`.

cc @victorsanni @justinmc

[Piinks]

Or, a great suggestion from @mit-mit:

One option is to improve the documentation comment on the library itself. We invested in this for a bunch of the Dart libraries last year. See e.g. these: https://api.dart.dev/dart-collection/ https://api.dart.dev/dart-math/
So we could have a section there on "raw widgets" and then list them out there