Automatically exclude the empty string as canonical keyword

This change carves out an exception to keyword canonicalization where if an enumerated attribute state maps to two keywords, with one of them being the empty string, then the canonical keyword is automatically the other keyword.

Fixes #11297 and fixes #11298.

Author: keithamus

source

@@ -5193,6 +5193,10 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
    <li><p>If there is only one <em>conforming</em> keyword mapping to the given state, then it is
    that conforming keyword.</p></li>
 
+   <li><p>If there are two conforming keywords mapping to the given state, and one is the empty
+   string, then the canonical keyword will be the conforming keyword that is not the empty
+   string.</p></li>
+
    <li><p>Otherwise, the canonical keyword for the state will be explicitly given in the
    specification for the attribute.</p></li>
   </ul>
@@ -7585,10 +7589,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
   <p>The attribute's <i data-x="missing value default">missing value default</i> is the <dfn
   data-x="attr-crossorigin-none">No CORS</dfn> state, and its <i data-x="invalid value
   default">invalid value default</i> is the <span
-  data-x="attr-crossorigin-anonymous">Anonymous</span> state. For the purposes of <span
-  data-x="reflect">reflection</span>, the <span>canonical keyword</span> for the <span
-  data-x="attr-crossorigin-anonymous">Anonymous</span> state is the <code
-  data-x="attr-crossorigin-anonymous-keyword">anonymous</code> keyword.</p>
+  data-x="attr-crossorigin-anonymous">Anonymous</span> state.</p>
 
   <p>The majority of fetches governed by <span data-x="CORS settings attribute">CORS settings
   attributes</span> will be done via the <span>create a potential-CORS request</span> algorithm.</p>