Remove concept of "expressly inert"

It seems a remnant of control groups, which were removed in whatwg#3647.
All uses are replaced with the concept of "inert".

Also cleaning up "When a key event is to be routed in a top-level
browsing context", which also seems to have remnants of when control
groups allowed inert elements inside an inert dialog to be focusable.

Fixes whatwg#7564.

source

@@ -74904,10 +74904,6 @@ END:VCARD</pre>
   <span>nested browsing context</span>'s <span>active document</span>, and all nodes in that
   <code>Document</code>, must be marked as <span>inert</span>.</p>
 
-  <p><span id="expressly-inert-control"></span><span id="expressly-inert-dialog"></span>An element
-  is <dfn>expressly inert</dfn> if it is <span>inert</span> and its <span>node document</span> is
-  not <span>inert</span>.</p>
-
   <p>A <code>Document</code> <var>document</var> is <dfn>blocked by a modal dialog</dfn>
   <var>subject</var> if <var>subject</var> is the topmost <code>dialog</code> element in
   <var>document</var>'s <span>top layer</span>. While <var>document</var> is so blocked, every node
@@ -75245,7 +75241,7 @@ END:VCARD</pre>
 
       <li>the element is not <span data-x="concept-element-disabled">actually disabled</span>;</li>
 
-      <li>the element is not <span>expressly inert</span>;</li>
+      <li>the element is not <span>inert</span>;</li>
 
       <li>the element is either <span>being rendered</span> or <span>being used as relevant canvas
       fallback content</span>.</li>
@@ -75262,8 +75258,7 @@ END:VCARD</pre>
     <tr>
      <th class="data-header" headers="th-fa-area" id="td-fa-2">
      The shapes of <code>area</code> elements in an <span>image map</span> associated with an
-     <code>img</code> element that is <span>being rendered</span> and is not <span>expressly
-     inert</span>.
+     <code>img</code> element that is <span>being rendered</span> and is not <span>inert</span>.
      <td headers="td-fa-2 th-fa-dom-rep">
      The <code>img</code> element.
     <tr>
@@ -75283,8 +75278,7 @@ END:VCARD</pre>
     <tr>
      <th class="data-header" headers="th-fa-area" id="td-fa-3">
      The user-agent provided subwidgets of elements that are <span>being rendered</span> and are not
-     <span data-x="concept-element-disabled">actually disabled</span> or <span>expressly
-     inert</span>.
+     <span data-x="concept-element-disabled">actually disabled</span> or <span>inert</span>.
      <td headers="td-fa-3 th-fa-dom-rep">
      The element for which the <span>focusable area</span> is a subwidget.
     <tr>
@@ -75299,9 +75293,9 @@ END:VCARD</pre>
     <tr>
      <th class="data-header" headers="th-fa-area" id="td-fa-4">
      The scrollable regions of elements that are <span>being rendered</span> and are not
-     <span>expressly inert</span>. <!-- the being rendered part is kinda
-     redundant, a scrollable region is a box generated for the element so by definition if the
-     element has a scrollable region it is being rendered -->
+     <span>inert</span>. <!-- the being rendered part is kinda redundant, a scrollable region is a
+     box generated for the element so by definition if the element has a scrollable region it is
+     being rendered -->
      <td headers="td-fa-4 th-fa-dom-rep">
      The element for which the box that the scrollable region scrolls was created.
     <tr>
@@ -76034,8 +76028,8 @@ END:VCARD</pre>
   <p><dfn>Focus fixup rule</dfn>: When the designated <span data-x="focused area of the
   document">focused area of the document</span> is removed from that <code>Document</code> in some
   way (e.g. it stops being a <span>focusable area</span>, it is removed from the DOM, it becomes
-  <span>expressly inert</span>, etc.), designate the <code>Document</code>'s <span>viewport</span>
-  to be the new <span>focused area of the document</span>.</p>
+  <span>inert</span>, etc.), designate the <code>Document</code>'s <span>viewport</span> to be the
+  new <span>focused area of the document</span>.</p>
 
   <p class="example">For example, this might happen because an element is removed from its
   <code>Document</code>, or has a <code data-x="attr-hidden">hidden</code> attribute added. It might
@@ -76171,8 +76165,7 @@ END:VCARD</pre>
    data-x="tlbc system focus">system focus</span>.</p></li>
 
    <li><p>If <var>target area</var> is a <span>focusable area</span>, let <var>target
-   node</var> be <var>target area</var>'s <span>DOM anchor</span>. Otherwise, <var>target area</var> is a <code>dialog</code>; let <var>target node</var> be
-   <var>target area</var>.</p></li>
+   node</var> be <var>target area</var>'s <span>DOM anchor</span>.</p></li>
 
    <li>
     <p>If <var>target node</var> is a <code>Document</code> that has a <span data-x="the
@@ -76186,13 +76179,6 @@ END:VCARD</pre>
 
    <li>
     <p>If <var>target node</var> is not <span>inert</span>, then:</p>
-
-    <p class="note">It is possible for the <span>currently focused area of a top-level browsing
-    context</span> to be <span>inert</span>, for example if a <span
-    data-x="dom-dialog-showModal">modal dialog is shown</span>, and then that <code>dialog</code>
-    element is made <span>inert</span>. It is likely to be the result of a logic error in the
-    application, though.</p>
-
     <ol>
      <li><p>Let <var>canHandle</var> be the result of <span
      data-x="concept-event-dispatch">dispatching</span> the key event at <var>target
@@ -128185,6 +128171,7 @@ INSERT INTERFACES HERE
   Olli Pettay,
   Ondřej Žára, <!-- ondras on GitHub -->
   Ori Avtalion,
+  Oriol Brufau,
   oSand, <!-- from reddit -->
   Pablo Flouret,
   Patrick Dark,