Don't change focus when re-focusing delegatesFocus shadow host

Doing otherwise causes https://github.com/web-platform-tests/wpt/blob/4c24c9acd809eb8630e795e3f8e3a787d9d6d039/html/semantics/interactive-elements/the-dialog-element/dialog-focus-shadow-double-nested.html to fail on the document.activeElement check.

This matches some previous discussions in WICG/webcomponents#840 and whatwg#5039.

source

@@ -76781,9 +76781,11 @@ partial interface <span id="NavigatorUserActivation-partial">Navigator</span> {
 
    <dd>
     <ol>
-     <li><p>If <var>focus target</var> is a <span>shadow-including inclusive ancestor</span> of the
-     <span>currently focused area of a top-level traversable</span>'s <span>DOM anchor</span>, then
-     return null.</p></li>
+     <li><p>Let <var>focusedElement</var> be the <span>currently focused area of a top-level
+     traversable</span>'s <span>DOM anchor</span>.</p></li>
+
+     <li><p>If <var>focus target</var> is a <span>shadow-including inclusive ancestor</span> of
+     <var>focusedElement</var>, then return <var>focusedElement</var>.</p></li>
 
      <li><p>Return the <span>focus delegate</span> for <var>focus target</var> given <var>focus
      trigger</var>.</p></li>