Fix object literal constructors where parameters need to be renamed

[srujzs]

External named parameter constructors create an object with the given names as keys and the arguments as values. Certain keywords are reserved by Dart, however, like is, and require a rename. We can do renaming of properties via @JS, but no such mechanism exists for the constructor. This seems to only affect a handful of dictionaries e.g.

web/lib/src/dom/dom.dart

Line 2386 in ff7185c

external factory ElementCreationOptions({String is_});

.