Add the "Perceptual" and "Classic" families of gradient spaces with OkLab as the new default (#4415)

* Add an OkLab gradient interpolation space and make it the new default

* Fix the Properties panel fill row resetting the gradient interpolation space to the default

* Add OkLch, Lab, LCh, and HSL gradient interpolation spaces

* Add a hue direction attribute and picker choice for polar gradient interpolation spaces

* Add an HSV gradient interpolation space

* Rename the sRGB Linear and sRGB Gamma gradient spaces to RGB Linear and RGB Gamma

* Divide the gradient interpolation dropdown between absolute and relative color spaces

* Rename the OkLch gradient interpolation space to OkLCh for channel-notation capitalization

* Shorten the color picker popover's hue direction row label to Arc

* Call the Gradient Interpolation node's parameter Space and extend the picker tooltip title to match

* Rename the gradient interpolation attribute and type family to gradient space

* Rename the gradient tool's gradient space transform to gradient to viewport transform

* Add serde aliases and a node replacement covering the gradient space renames

* Give the gradient space choices artist-facing labels and reorder the dropdown sections

* Add a Gradient Hue Direction node and its attribute read node

* Say interpolate instead of blend for gradient stop color traversal in docs and tooltips

* Label the polar perceptual gradient spaces as Perceptual Hue and group the dropdown sections by geometry

* Add a migration alias covering the gradient space attribute reader rename

* Carry the gradient hue direction attribute through boolean operations

* Register GradientHueDirection wire types in the node registry

Cargo.lock

@@ -6599,6 +6599,7 @@ version = "0.1.0"
 dependencies = [
  "bitflags 2.11.0",
  "bytemuck",
+ "color",
  "core-types",
  "dyn-any",
  "fixedbitset",