fix(reusePaths): dont reuse id if referenced in href

[SethFalco]

Fixes a bug where the reusePaths plugin would reuse the node ID that it's optimizing, but that ID was also referenced in a href elsewhere in the document, so it unintentionally applied the path to other nodes.

Example

<svg xmlns="http://www.w3.org/2000/svg"
  xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="-29.947 60.987 69.975 102.505">
  <g transform="translate(-59 64)">
    <g id="b">
      <path id="a" fill="#000" d="M0 0v1h.5Z" transform="rotate(18 3.157 -.5)"/>
      <use xlink:href="#a" width="1" height="1" transform="scale(-1 1)"/>
    </g>
    <use xlink:href="#b" width="1" height="1" transform="rotate(72)"/>
    <use xlink:href="#b" width="1" height="1" transform="rotate(-72)"/>
    <use xlink:href="#b" width="1" height="1" transform="rotate(144)"/>
    <use xlink:href="#b" width="1" height="1" transform="rotate(-144)"/>
  </g>
  <path id="c" fill="#000" d="M0 0v1h.5Z" transform="rotate(18 3.157 -.5)"/>
  <use xlink:href="#c" width="1" height="1" transform="scale(-1 1)"/>
</svg>

In this document, svg g g path#a and svg path#c both have a reusable path. Before, since the first path has an ID, the behavior was that it would take and reuse that.

But that's not ideal in this case, because svg g g use[xlink:href] is referencing #a already. By making that change, it changed what that node was referencing to an entirely different path.

This PR checks if the ID is already being referenced by another node. If so, create a new ID anyway instead of reusing and deleting the existing one.

Related

• Closes reusePaths breaks file #1733
• Will cause conflicts for fix(reusePaths): reuse defs tag if exists and remove redundant nodes #1785 (I'll just fix them, no worries.)

Notes

• When set as a default plugin, test-regression had 3 mismatches before, still at 3.