Rename :open to :popover-open and remove :closed

As discussed in w3c/csswg-drafts#8637.

Tests: web-platform-tests/wpt#39222.

source

@@ -72496,24 +72496,15 @@ Demos:
     not null, or containing no elements, if it is. <ref spec=SELECTORS></p>
    </dd>
 
-   <dt><dfn selector noexport><code data-x="selector-open">:open</code></dfn></dt>
+   <dt><dfn selector noexport><code data-x="selector-popover-open">:popover-open</code></dfn></dt>
    <dd>
-    <p>The <code data-x="selector-open">:open</code> <span>pseudo-class</span> is defined to match
-    any <span data-x="html elements">HTML element</span> whose <code
+    <p>The <code data-x="selector-popover-open">:popover-open</code> <span>pseudo-class</span> is
+    defined to match any <span data-x="html elements">HTML element</span> whose <code
     data-x="attr-popover">popover</code> attribute is not in the <span
     data-x="attr-popover-none-state">no popover state</span> and whose <span>popover visibility
     state</span> is <span data-x="popover-showing-state">showing</span>.</p>
    </dd>
 
-   <dt><dfn selector noexport><code data-x="selector-closed">:closed</code></dfn></dt>
-   <dd>
-    <p>The <code data-x="selector-closed">:closed</code> <span>pseudo-class</span> is defined to
-    match any <span data-x="html elements">HTML element</span> whose <code
-    data-x="attr-popover">popover</code> attribute is not in the <span
-    data-x="attr-popover-none-state">no popover state</span> and whose <span>popover visibility
-    state</span> is <span data-x="popover-hidden-state">hidden</span>.</p>
-   </dd>
-
    <dt><dfn selector noexport><code data-x="selector-enabled">:enabled</code></dfn></dt>
    <dd>
     <p>The <code data-x="selector-enabled">:enabled</code> <span>pseudo-class</span> must match any
@@ -123590,10 +123581,11 @@ dialog::backdrop {
   background: rgba(0,0,0,0.1);
 }
 
-[popover]:closed:not(dialog[open]) {
+[popover]:not(:popover-open):not(dialog[open]) {
   display:none;
 }
-dialog[popover]:not(:closed) {
+
+dialog:popover-open {
   display:block;
 }
 
@@ -123610,7 +123602,7 @@ dialog[popover]:not(:closed) {
   background-color: Canvas;
 }
 
-[popover]:open::backdrop {
+:popover-open::backdrop {
   position: fixed;
   inset: 0;
   pointer-events: none !important;