LibWeb+LibURL: Consolidate Origin parsing and serialization into LibURL

Because of the previous awkward factoring of Origin we had two
implementations of Origin serializing and creation. Move the
implementation of DOMURL::url_origin into URL::origin, and
instead use the implemenation of URL::Origin::serialize for
serialization (replacing URL::serialize_origin).

This happens to fix 8 URL subtests as the two implemenations had
diverged, and URL::serialize_origin was previously missing the spec
changes of: whatwg/url@eee49fd and whatwg/url@fff33c3

Userland/Libraries/LibWeb/StorageAPI/StorageKey.cpp

@@ -36,7 +36,7 @@ StorageKey obtain_a_storage_key_for_non_storage_purposes(HTML::Environment const
         auto& mutable_settings = const_cast<HTML::EnvironmentSettingsObject&>(settings);
         return { mutable_settings.origin() };
     }
-    return { DOMURL::url_origin(environment.creation_url) };
+    return { environment.creation_url.origin() };
 }
 
 }