With all the plumbing in place, we can handle this quirk at the
serialization layer.
This allows us to remove the pass where StyleComputer would loop over
all computed values and replace any color values with new values
stripped of their original name strings.
Fixes the crash in css/css-color/parsing/color-valid-hwb.html.
The crash was probably introduced in 248e4bb5, as it was the first
commit to VERIFY that the value given to `Color::with_opacity` were in
the correct range. As the values in color-valid-hwb.html were resolved
as NaN, the check never passed.
When serializing an sRGB color value that originated from a named color,
it should return the color name converted to ASCII lowercase. This
requires storing the color name (if it has one).
This change also requires explicitly removing the color names when
computing style, because computed color values do not retain their name.
It also requires removing a caching optimization in create_from_color(),
because adding the name means that the cached value might be wrong.
This fixes some WPT subtests, and also required updating some of our own
tests.
