It's now set through the intermediate InterfaceConstructorBehavior structure,
which lets us improve the abstraction around NonCallbackInterfaceObjectClass
a bit better.
When the interface's constructor is supposed to always throw, the error for
calling `Foo()` without new is "Illegal constructor.". when the interface
actually defines an interface, the error is instead
"This constructor needs to be called with `new`.".
The function do_create_interface_objects is removed in favour of 4 functions:
create_callback_interface_object, create_interface_prototype_object,
create_noncallback_interface_object and create_named_constructors.
While this increases the amount of codegen'd code, this greatly improves the
readability of the code involved in this part of DOM, instead of having one function
doing 4 different things. We can always find a more adequate abstraction later.
NativeProperties and everything related to the interface objects have been removed
from the utils module.
