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)

node-graph/graph-craft/src/document/value.rs

@@ -555,9 +555,9 @@ tagged_value! {
 	GradientForm(vector::style::GradientForm),
 	#[serde(alias = "GradientSpreadMethod")] // TODO: Eventually remove this document upgrade code
 	GradientSpread(vector::style::GradientSpread),
-	#[serde(alias = "GradientInterpolation")] // TODO: Eventually remove this document upgrade code
 	GradientSpace(vector::style::GradientSpace),
 	GradientHueDirection(vector::style::GradientHueDirection),
+	GradientInterpolation(vector::style::GradientInterpolation),
 	ReferencePoint(vector::ReferencePoint),
 	CentroidType(vector::misc::CentroidType),
 	BooleanOperation(vector::misc::BooleanOperation),