This patch just adds the new root paintable and updates the tests
expectations. The next patch will move painting logic from the layout
viewport to the paint viewport.
Using fixed-point saturated arithmetics for CSSPixels allows to avoid
accumulating floating-point errors.
This implementation is not complete yet: currently saturated
arithmetics implemented only for addition. But it is enough to not
regress any of layout tests we have :)
See https://github.com/SerenityOS/serenity/issues/18566
All of the following properties in the font shorthand can be `normal`:
- font-style
- font-variant
- font-weight
- font-stretch
This means that we must allow up to four consecutive `normal` at the
start of a font shorthand value.