Since we resolve any relative lengths at compute time there's no need
for the value to be passed around as a `NumberOrCalculated` and we can
just resolve it within `ComputedProperties::font_variation_settings`.
The only place this is used it is used with value_or so there's no need
to return it is an `Optional`.
This is only used for loading fonts (which occurs during style
computation) so there's no need to store it in `ComputedValues`
Integrates the new `FontVariationSettings` from LibGfx into LibWeb to
enable initial variable font functionality. Currently, only the `wght`
(weight) axis is fully supported and tested. This update also introduces
support for the CSS `font-variation-settings` property.
