Add script-supporting elements

https://html.spec.whatwg.org/multipage/dom.html#script-supporting-elements-2

Author: toastal

lib/html_types.mli

@@ -427,6 +427,8 @@ type formassociated = [ | listed | `Progress | `Meter | `Label ]
 type subresource_integrity = [ | `Crossorigin | `Integrity ]
 (** @see <https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity> *)
 
+type script_supporting = [ | `Script | `Template ]
+
 (** Transparent elements.
     Such elements have a part of they children in their data
     and behaves like them. We could do something like [a: 'a elt list -> 'a elt]