Expand color stops during display list recording rather than playback.
Recording happens once but the display list may be executed many times,
so doing this work at record time is more efficient.
This lets us not care about non-absolute Length units when resolving
gradient data, as they'll already have been converted to px.
We can also use Angle::from_style_value() safely on absolutized angles,
which reduces some boilerplate code.
A few things fall out of this:
- We no longer need to templatize our color-stop list types.
- A bit more code is required to resolve gradient data.
This results in a slightly different rendering for a couple of the test
gradients, with a larger difference between macOS and Linux. I've
expanded the fuzziness factor to cover for it.
Using a generic context argument will allow us to resolve colors in
places where we have all the required information but not in the form of
a layout node as was expected previously.
`CSSColorValue`s which have unresolved `calc` components should be able
to be resolved. Previously we would always resolve them but with
incorrect values.
This is useful as we will now be able to now whether we should serialize
colors in their normalized form or not.
Slight regression in that we now serialize (RGB, HSL and HWB) colors
with components that rely on compute-time information as an empty
string, but that will be fixed in the next commit.
None of the code here actually needs a NodeWithStyleAndBoxModelMetrics,
and we'll need to be able to resolve images from inside
NodeWithStyle::apply_style().
The Web::CSS::Parser's GradientParsing ignores color-stops if
it is only a single one. This change allows to have color-stops
with double positions against a single color.
Further, also allows for `linear-gradient(black)` and similar
other gradient functions
