Ignore DOM state when hiding popovers if needed

Fixes whatwg#9161
Fixes whatwg#9367
Makes obsolete whatwg/dom#1185

This PR prevents the hide popover algorithm from returning early when
the popover attribute is removed or when the element with the popover
attribute is removed from the document.

The fireEvents parameter is used as an indicator that either the element
is being removed or that the attribute is being removed, and when it is
false, the calls to check popover validity are replaced with a check to
simply see if the popover is already hidden.

This patch also makes removal of the popover attribute stop firing
events in order to signal to the hide popover algorithm that checks for
the popover attribute should be ignored.

source

@@ -82409,9 +82409,11 @@ dictionary <dfn dictionary>DragEventInit</dfn> : <span>MouseEventInit</span> {
    <li><p>If <var>localName</var> is not <code data-x="attr-popover">popover</code>, then
    return.</p></li>
 
+   <li><p>Let <var>fireEvents</var> be false if <var>value</var> is null, otherwise true.</p></li>
+
    <li><p>If <var>oldValue</var> and <var>value</var> are in different <span
    data-x="attr-popover">states</span>, then run the <span>hide popover algorithm</span> given
-   <var>element</var>, true, true, and false.</p></li>
+   <var>element</var>, true, <var>fireEvents</var>, and false.</p></li>
   </ol>
 
   <dl class="domintro">
@@ -82613,8 +82615,12 @@ dictionary <dfn dictionary>DragEventInit</dfn> : <span>MouseEventInit</span> {
   boolean <var>fireEvents</var>, and a boolean <var>throwExceptions</var>:</p>
 
   <ol>
-   <li><p>If the result of running <span>check popover validity</span> given <var>element</var>,
-   true, <var>throwExceptions</var>, and null is false, then return.</p></li>
+   <li><p>If <var>fireEvents</var> is true and the result of running <span>check popover
+   validity</span> given <var>element</var>, true, <var>throwExceptions</var>, and null is false,
+   then return.</p></li>
+
+   <li><p>If <var>fireEvents</var> is false and <var>element</var>'s <span>popover visibility
+   state</span> is <span data-x="popover-hidden-state">hidden</span>, then return.</p></li>
 
    <li><p>Let <var>document</var> be <var>element</var>'s <span>node document</span>.</p></li>
 
@@ -82643,15 +82649,19 @@ dictionary <dfn dictionary>DragEventInit</dfn> : <span>MouseEventInit</span> {
      <var>element</var>, <var>focusPreviousElement</var>, and <var>fireEvents</var>.</p></li>
 
      <li>
-      <p>If the result of running <span>check popover validity</span> given <var>element</var>,
-      true, and <var>throwExceptions</var> is false, then run <var>cleanupHidingFlag</var> and
-      return.</p>
+      <p>If <var>fireEvents</var> is true and the result of running <span>check popover
+      validity</span> given <var>element</var>, true, and <var>throwExceptions</var> is false, then
+      run <var>cleanupHidingFlag</var> and return.</p>
 
       <p class="note"><span>Check popover validity</span> is called again because running <span
       data-x="hide-all-popovers-until">hide all popovers until</span> could have disconnected
       <var>element</var> or changed its <code data-x="attr-popover">popover</code> attribute.</p>
      </li>
 
+     <li><p>If <var>fireEvents</var> is false and <var>element</var>'s <span>popover visibility
+     state</span> is <span data-x="popover-hidden-state">hidden</span>, then run
+     <var>cleanupHidingFlag</var> and return.</p></li>
+
      <li><p>If the last item in <var>document</var>'s <span>auto popover list</span> is
      <var>element</var>, then <span>break</span>.</p></li>
     </ol>