The approach of attaching sub-widgets to the web view widget was only
ever going to work in single-process mode, and that's not what we're
about anymore, so let's just get rid of WidgetBox so we don't have the
dead-end architecture hanging over us.
The next step here is to re-implement <input type=text> using LibWeb
primitives.
From https://dom.spec.whatwg.org/#concept-getelementsbyclassname:
The comparisons for the classes must be done in an ASCII case-
insensitive manner if root’s node document’s mode is "quirks", and
in an identical to manner otherwise.
