SMIL node sorting should account for shadow dom elements

Differential Revision: https://phabricator.services.mozilla.com/D254343

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1957178
gecko-commit: 272a0b7231fdfe16495e2b65671017c242b5bc32
gecko-reviewers: emilio

Author: longsonr

svg/animations/crashtests/firefox-bug-1957178.html

@@ -0,0 +1,10 @@
+<script>
+window.addEventListener("DOMContentLoaded", () => {
+  a.insertAdjacentHTML("beforeEnd", b.innerHTML)
+})
+</script>
+<basefont id="a"></basefont>
+<menu id="b">
+<svg id="c">
+<use xlink:href="#c">
+<animateMotion xlink:href="#c" />