Auto block heights are now computed according to something that kinda
resembles the specification.
Blocks with inline children and height:auto have their height computed
based on the top of the first line box and the bottom of the last line
box. Very straightforward.
Blocks with block children and height:auto have their height computed
based on the top of the first in-flow block child's margin box, and the
bottom of the last in-flow block child's margin box.
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
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.
