Add a gradient interpolation attribute with Stepped, Linear (existing), and Smooth modes (#4418)

* Delete dead code function

* Add a Gradient Interpolation axis with Stepped, Linear, and Smooth paths through the stops

* Keep the gradient interpolation attached when dragging stops in the picker

* Give the gradient popover's dropdowns the same tooltips as their row labels

* Order the gradient popover with Intrp. above Space

* Hold gradient stops in place when the cyclic flag is toggled

* Fix wrong Smooth gradient colors around stops sitting on the ramp boundaries

* Consolidate gradient settings plumbing and fix bugs

* Bundle whole-ramp gradient settings into GradientSettings across the editor plumbing

* Name the Smooth gradient interpolation's spline type in its tooltip

* Linearize the gamma hex stop colors recovered from imported Graphite SVGs

* Code review

* Aim the Smooth bake's seam subdivision at the copied boundary color

* Add GradientEvaluator to build gradient sampling state once per loop instead of per sample

* Correct the gradient evaluator's documented setup cost to O(n log n)

editor/src/messages/portfolio/document_migration.rs

@@ -175,10 +175,6 @@ const NODE_REPLACEMENTS: &[NodeReplacement<'static>] = &[
 		node: graphene_std::graphic::read_attribute_gradient_spread::IDENTIFIER,
 		aliases: &["graphic_nodes::graphic::ReadAttributeSpreadMethodNode"],
 	},
-	NodeReplacement {
-		node: graphene_std::graphic::read_attribute_gradient_space::IDENTIFIER,
-		aliases: &["graphic_nodes::graphic::ReadAttributeGradientInterpolationNode"],
-	},
 	NodeReplacement {
 		node: graphene_std::graphic::remove_at_index::IDENTIFIER,
 		aliases: &["graphic_nodes::graphic::OmitElementNode"],
@@ -278,10 +274,6 @@ const NODE_REPLACEMENTS: &[NodeReplacement<'static>] = &[
 		node: graphene_std::math_nodes::gradient_form::IDENTIFIER,
 		aliases: &["math_nodes::GradientTypeNode"],
 	},
-	NodeReplacement {
-		node: graphene_std::math_nodes::gradient_space::IDENTIFIER,
-		aliases: &["math_nodes::GradientInterpolationNode"],
-	},
 	NodeReplacement {
 		node: graphene_std::math_nodes::gradient_spread::IDENTIFIER,
 		aliases: &["math_nodes::SpreadMethodNode"],