* Show accessibility frame while scrolling

* ++

* fix test

Diagnostics object is.

Fixes #11855

* a11y: handle left/right scrolls correctly

* fix keep alive test

* fix scaffold test

Refactor RenderObject.toStringDeep and Widget.toStringDeep code to use DiagnosticsNode.

* AutomaticKeepAlive

A Widget that listens for notifications from widgets that don't want to die.

* Automatically wrap SliverList and SliverGrid children in AutomaticKeepAlive widgets

* Fixes for review comments