Fix corner case invoker issue with popover nested inside invoker

In this situation:

```
<button popovertarget=foo>Activate
  <div popover id=foo>Clicking me shouldn't close me</div>
</button>
```

clicking the button properly activates the popover, however, clicking on the popover itself after that should **not** close the popover. It currently does because the popover click bubbles to the `<button>` and activates the invoker, which toggles the popover closed.

This patch fixes that case.

source

@@ -48192,8 +48192,9 @@ interface <dfn interface>HTMLInputElement</dfn> : <span>HTMLElement</span> {
    <li><p>Run <var>element</var>'s <dfn>input activation behavior</dfn>, if any, and do nothing
    otherwise.</p></li>
 
-   <li><p>Run the <span>popover target attribute activation behavior</span> on
-   <var>element</var>.</p></li>
+   <li><p>Run the <span>popover target attribute activation behavior</span> given
+   <var>element</var> and <var>event</var>'s
+   <span data-x="concept-event-target">target</span>.</p></li>
   </ol>
 
   <p class="note">Recall that an element's <span>activation behavior</span> runs for both
@@ -53491,7 +53492,8 @@ interface <dfn interface>HTMLButtonElement</dfn> : <span>HTMLElement</span> {
    </li>
 
    <li><p>Run the <span>popover target attribute activation behavior</span> given
-   <var>element</var>.</p></li>
+   <var>element</var> and <var>event</var>'s
+   <span data-x="concept-event-target">target</span>.</p></li>
   </ol>
 
   </div>
@@ -86359,13 +86361,16 @@ dictionary <dfn dictionary>DragEventInit</dfn> : <span>MouseEventInit</span> {
   attribute, <span>limited to only known values</span>.</p>
 
   <p>To run the <dfn>popover target attribute activation behavior</dfn> given a <code>Node</code>
-  <var>node</var>:</p>
+  <var>node</var> and an <code>EventTarget</code> <var>eventTarget</var>:</p>
 
   <ol>
    <li><p>Let <var>popover</var> be <var>node</var>'s <span>popover target element</span>.</p></li>
 
    <li><p>If <var>popover</var> is null, then return.</p></li>
 
+   <li><p>If <var>eventTarget</var> is a <span>shadow-including inclusive descendant</span> of
+   <var>popover</var>, then return.</p></li>
+
    <li><p>If <var>node</var>'s <code data-x="attr-popovertargetaction">popovertargetaction</code>
    attribute is in the <span data-x="attr-popovertargetaction-show">show</span> state and
    <var>popover</var>'s <span>popover visibility state</span> is <span