Editorial: make the type of custom element constructors stricter

customElement.define()'s 2nd argument "constructor" was defined as a
Function, but considering its use case in the "upgrade an element"
algorithm, the exact function type should be any ().

source

@@ -66310,12 +66310,14 @@ console.log(plasticButton.outerHTML); // will output '<button is="plastic-but
 
   <pre class="idl">[Exposed=Window]
 interface <dfn>CustomElementRegistry</dfn> {
-  [<span>CEReactions</span>] void <span data-x="dom-CustomElementRegistry-define">define</span>(DOMString name, Function constructor, optional ElementDefinitionOptions options);
+  [<span>CEReactions</span>] void <span data-x="dom-CustomElementRegistry-define">define</span>(DOMString name, <span>CustomElementConstructor</span> constructor, optional <span>ElementDefinitionOptions</span> options);
   any <span data-x="dom-CustomElementRegistry-get">get</span>(DOMString name);
   Promise&lt;void&gt; <span data-x="dom-CustomElementRegistry-whenDefined">whenDefined</span>(DOMString name);
   [<span>CEReactions</span>] void <span data-x="dom-CustomElementRegistry-upgrade">upgrade</span>(<span>Node</span> root);
 };
 
+callback <dfn>CustomElementConstructor</dfn> = any ();
+
 dictionary <dfn>ElementDefinitionOptions</dfn> {
   DOMString extends;
 };</pre>