Enhancement request: Allow the raster mark to use CSS4 colour specifications and the P3 colour space.

Marks that generate SVG currently work with modern colour specifications, meaning they can specify colours using new colour spaces such as Oklch. For example, this works correctly:

Plot.cellX([1], { fill: "oklch(52.6% 0.24 29.5deg)" }).plot()

Not only does this give access to improved perceptual colour spaces, but also allows deeply saturated colours outside the sRGB gamut but in the P3 gamut to be rendered correctly on displays that support P3 (with a graceful fallback to the nearest sRGB colour for those which don't).

However, the raster mark, which relies on Canvas, does not currently support either modern colour specification, nor the P3 colour space. The following renders a raster as black rather than the intended saturated red:

Plot.raster([1], {
  width: 1,
  height: 1,
  fill: "oklch(52.6% 0.24 29.5deg)"
}).plot()

It would be great to have support for modern colour specs in Canvas.

As far as I can see, the current implementation creates an sRGB canvas rather than a p3-friendly one. I think that would just require

getContext("2d", { colorSpace: "display-p3" });

But handling CSS 4 colour specs looks a little more tricky as the implementation seems to rely on d3.color which currently does not handle the modern comma-free colour format. I note d3 issue #87 though.