Fix dialog focus restoring descendant check

1429dac accidentally made the currently focused element check look for the element to restore focus on as an ancestor instead of the dialog element "subject". Correct this to look at the dialog element instead of the element to restore focus to.

This was identified at #9178 (comment).

Author: josepharhar

source

@@ -62249,7 +62249,7 @@ interface <dfn interface>HTMLDialogElement</dfn> : <span>HTMLElement</span> {
 
      <li><p>If <var>subject</var>'s <span>node document</span>'s <span>focused area of the
      document</span>'s <span>DOM anchor</span> is a <span>shadow-including inclusive
-     descendant</span> of <var>element</var>, or <var>wasModal</var> is true, then run the
+     descendant</span> of <var>subject</var>, or <var>wasModal</var> is true, then run the
      <span>focusing steps</span> for <var>element</var>; the viewport should not be scrolled by
      doing this step.</p></li>
     </ol>