Fix popover initial focus autofocus document targeting

Match the dialog processing model and use the more correct, modern framework of navigables instead of browsing contexts.

Closes #11187.

Author: josepharhar

source

@@ -87486,9 +87486,9 @@ dictionary <dfn dictionary>DragEventInit</dfn> : <span>MouseEventInit</span> {
 
    <li><p>Run the <span>focusing steps</span> given <var>control</var>.</p></li>
 
-   <li><p>Let <var>topDocument</var> be the <span>active document</span> of <var>control</var>'s
-   <span>node document</span>'s <span data-x="concept-document-bc">browsing context</span>'s
-   <span>top-level browsing context</span>.</p></li>
+   <li><p>Let <var>topDocument</var> be <var>control</var>'s <span>node navigable</span>'s <span
+   data-x="nav-top">top-level traversable</span>'s <span data-x="nav-document">active
+   document</span>.</p></li>
 
    <li><p>If <var>control</var>'s <span>node document</span>'s <span
    data-x="concept-document-origin">origin</span> is not the <span data-x="same origin">same</span>