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
While it's possible to getComputedStyle() on an unconnected element,
the resulting object is not supposed to have any values, since we can't
resolve style without a document root anyway.
This fixes a crash on https://bandcamp.com