Set media element official playback position immediately upon seeking

This change ensures that the new playback position on the valid media timeline is observable immediately following an assignment to a media element's currentTime attribute. It will also be immediately observable after calling fastSeek().

Fixes #11773

Author: Zaggy1024

source

@@ -39080,9 +39080,10 @@ interface <dfn interface>MediaError</dfn> {
   data-x="dom-media-readyState">readyState</code> is <code
   data-x="dom-media-HAVE_NOTHING">HAVE_NOTHING</code>, then it must set the <span>media
   element</span>'s <span>default playback start position</span> to the new value; otherwise, it must
-  set the <span>official playback position</span> to the new value and then <span
-  data-x="dom-media-seek">seek</span> to the new value. The new value must be interpreted as being
-  in seconds.</p>
+  <span data-x="dom-media-seek">seek</span> to the new value. The new value must be interpreted as
+  being in seconds. The value returned upon setting must be the new value, not the official playback
+  position after it has been modified by the synchronous steps of the <span
+  data-x="dom-media-seek">seek</span>.</p>
   </div>
 
   <p>If the <span>media resource</span> is a streaming resource, then the user agent might be unable
@@ -40378,11 +40379,6 @@ interface <dfn interface>MediaError</dfn> {
 
    <li><p>Set the <code data-x="dom-media-seeking">seeking</code> IDL attribute to true.</p></li>
 
-   <li><p>If the seek was in response to a DOM method call or setting of an IDL attribute, then
-   continue the script. The remainder of these steps must be run <span>in parallel</span>. With the exception
-   of the steps marked with &#x231B;, they could be aborted at any time by another instance of this
-   algorithm being invoked.</p></li>
-
    <li><p>If the <var>new playback position</var> is later than the end of the <span>media
    resource</span>, then let it be the end of the <span>media resource</span> instead.</p></li>
 
@@ -40399,6 +40395,14 @@ interface <dfn interface>MediaError</dfn> {
    data-x="dom-media-seekable">seekable</code> attribute, then set the <code
    data-x="dom-media-seeking">seeking</code> IDL attribute to false and return.</p></li>
 
+   <li><p>Set the <span>official playback position</span> to the <var>new playback
+   position</var>.</p></li>
+
+   <li><p>If the seek was in response to a DOM method call or setting of an IDL attribute, then
+   continue the script. The remainder of these steps must be run <span>in parallel</span>. With the exception
+   of the steps marked with &#x231B;, they could be aborted at any time by another instance of this
+   algorithm being invoked.</p></li>
+
    <li>
     <p>If the <i>approximate-for-speed</i> flag is set, adjust the <var>new playback
     position</var> to a value that will allow for playback to resume promptly. If <var>new