Read the descriptor style values instead of producing a ParsedFontFace
first, as this means we know if a descriptor is actually present, or
has been defaulted to an initial value. This lets us correctly skip the
unicode-range if it was not explicitly set.
Firefox and Chromium both serialize using the "font-stretch" name,
(which is an alias for font-width) which follows the outdated cssom
spec, so I've done so too to match them.
The one thing that we still do differently in this test is that those
browsers check explicitly if `font-stretch` was set, and ignore when
`font-width` is.
I've also inlined the `serialize_a_local()` function to the one place
it's used. The style value to_string() method was already wrapping the
string in quotes, so calling serialize_a_string() on it was producing
`local("\this mess\"")`. It's clearer what's happening when the code
isn't split up.
The WPT tests require the shortest possible serialization that support
an 8 bits roundtrip.
As an example, `128` is serialized to `0.5` while `127` needs more
precision and thus will be serialized to `0.498`.
This commit fixes 33 WPT subtests in css/css-color.
