Finalize and unify the design of the 'Morph' and 'Blend' nodes (#3974)

* Fix Morph node transform interpolation and preservation in the table

* Fix click target positions for Morph's nested layers by pre-compensating upstream_data transforms

* Redesign Morph node (v3) with control path input and uniformly spaced progression, and fix Stroke::lerp interpolation weights

* Add migration from Morph node v2 to v3

* Redesign the 'Blend Shapes' node behavior and subgraph definition

* Add the Layer > Blend menu entry to easily set up a blend

* Optimize the Morph node

* Refactor the Morph node to remove the roundtrip through BezPath

* Fine-tune Morph node Bezier order promotion and handle interpolation

* Add the Layer > Morph menu bar entry

* Fix NaN and guard against other potential NaN bugs breaking the editor

* Add InterpolationDistribution parameter to Morph with weighted progression, swap parameter orders, and rename shear to skew

* Add the Reverse parameter to the Morph node

* Update the order of the inputs to Blend Shapes for consistency with Morph

* Make Layer > Morph create the Morph Path control layer

* Fix migrations

* Move 10 to a constant

* Avoid division by 0 in the Blend Shapes node internals

* Rename nodes 'Blend' -> 'Mix' and 'Blend Shapes' to 'Blend'

* Fix a crash encountered while testing

* Final code review

* Make domain push dupe checks debug-only and use push_unchecked in the Morph node

* Pre-allocate for pushes to the vector domains

* Add fast path at t=0

* Inline reserve()

* Set up the control path layer above not below, and starting collapsed

* Review fixes

---------

Co-authored-by: Timon <me@timon.zip>

website/content/features.md

@@ -138,7 +138,7 @@ Marrying vector and raster under one roof enables both art forms to complement e
 			<img class="atlas" style="--atlas-index: 66" src="https://static.graphite.art/icons/icon-atlas-roadmap__5.png" alt="" />
 			<span>All-around performance optimizations</span>
 		</div>
-		<div class="feature-icon ongoing" title="Development Ongoing">
+		<div class="feature-icon complete" title="Development Complete">
 			<img class="atlas" style="--atlas-index: 73" src="https://static.graphite.art/icons/icon-atlas-roadmap__5.png" alt="" />
 			<span>Blend tool to morph between shapes</span>
 		</div>