Fixed C code generation for polymorphic calls where the target is expanded.
Fixed bug in generated C code for TYPE.new_instance and TYPE.new_special_any_instance when dealing with expanded types and type instances.
Improved implementation of TYPE.new_instance and TYPE.new_special_any_instance by making it possible to restrict the size of dynamic type sets. This is done by providing the list of types which can have instances created by these two features.