Initial implementation of ownPropertyKeys proxy handler

Generates `SupportedPropertyNames` on DOM structs that should implement
it. Most of them are unimplemented now (which can be implemented in
later PRs), with the exception of `HTMLCollection`. Also added a couple
relevant WPT tests.

Closes #6390

Closes #2215

components/script/dom/document.rs

@@ -1912,6 +1912,12 @@ impl<'a> DocumentMethods for &'a Document {
         collection.r().reflector().get_jsobject().get()
     }
 
+    // https://html.spec.whatwg.org/#document
+    fn SupportedPropertyNames(self) -> Vec<DOMString> {
+        // FIXME: unimplemented (https://github.com/servo/servo/issues/7273)
+        vec![]
+    }
+
     global_event_handlers!();
     event_handler!(readystatechange, GetOnreadystatechange, SetOnreadystatechange);
 }