Sanitizer: Remove rel attribute from a element.

Implements WICG/sanitizer-api#346

Differential Revision: https://phabricator.services.mozilla.com/D270492

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1997085
gecko-commit: fe88f0f4c6f26fbe8e8a311f3ce2f60863155b8d
gecko-reviewers: freddyb

Author: evilpie

sanitizer-api/sethtml-tree-construction.sub.dat

@@ -646,3 +646,9 @@ test<div>p</div>tt<p>div</p><test>test</test>
 |   content
 |     "Hello"
 
+#data
+<a href="about:blank" rel="opener">Click.</a>
+#document
+| <a>
+|   href="about:blank"
+|   "Click."