Stop passing State objects between widgets in the LayoutExplorer

[jacob314]

The layout explorer uses an anti-pattern where State objects are passed between widgets for convenience.
These uses should be cleaned up passing around Controllers, callbacks, or using InheritedWidget instead.

[elliette]

We still have this anti-pattern, see for example here:

devtools/packages/devtools_app/lib/src/screens/inspector/layout_explorer/box/box.dart

Line 376 in 95e2baa

required this.state,