(bullet 2) 2 disjuncts, a type and a constant: put type before constant

(duplicates the first commit in PR #2995)

spec.html

@@ -42784,7 +42784,7 @@ <h1>
             _state_: a JSON Serialization Record,
             _key_: a String,
             _holder_: an Object,
-          ): either a normal completion containing either *undefined* or a String, or a throw completion
+          ): either a normal completion containing either a String or *undefined*, or a throw completion
         </h1>
         <dl class="header">
         </dl>