fix(Vectorizer): handle nested SVG in getRelativeTransformation()

[kumilingus]

Problem

getRelativeTransformation() returned null for elements that span a nested <svg> boundary. This is because it compared the immediate ownerSVGElement of each node, which differs when one element is inside a nested <svg>:

<svg id="root">                        <!-- ownerSVGElement: null -->
  <g id="A" transform="translate(10,20)">  <!-- ownerSVGElement: #root -->
    <g>
      <svg id="nested" x="30" y="40">     <!-- ownerSVGElement: #root -->
        <g transform="translate(5,5)">     <!-- ownerSVGElement: #nested  ← different! -->
          <rect id="B" />                  <!-- ownerSVGElement: #nested  ← different! -->
        </g>
      </svg>
    </g>
  </g>
</svg>

Calling V(A).getTransformToElement(B) would return null because A.ownerSVGElement (#root) !== B.ownerSVGElement (#nested), even though both elements live in the same document.

Fix

• Added getRootSVG() helper that walks the ownerSVGElement chain up to the root <svg>, so both A and B resolve to #root
• getRootSVG() returns null for detached non-SVG elements, and getRelativeTransformation() handles this gracefully
• Added regression test asserting expected matrix translation values across a nested <svg> boundary

[Copilot]

Pull request overview

Fixes Vectorizer’s relative transform calculation across nested <svg> boundaries by comparing root SVG containers rather than immediate ownerSVGElement, and adds a regression test to cover the scenario.

Changes:

• Add getRootSVG() helper and use it in getRelativeTransformation() to support nested SVG hierarchies.
• Add QUnit test validating getTransformToElement() behavior across a nested <svg>.
• Update external SVG images example (highlighter options) and add Volta toolchain pins.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
packages/joint-core/src/V/transform.mjs	Adjusts root-SVG comparison logic via getRootSVG() to avoid returning null across nested SVG boundaries.
packages/joint-core/test/vectorizer/vectorizer.js	Adds regression test for nested SVG transformation behavior.
examples/external-svg-images-js/src/main.js	Changes example highlighter configuration (nonScalingStroke).
examples/external-svg-images-js/package.json	Adds Volta toolchain pinning for the example.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

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