Replace the `Field` attribute with a named `_FieldDescriptor`.

        .. note::
            This method is called  during construction of the `Model`.

def add_to_class(self, model_class):
        """Replace the `Field` attribute with a named `_FieldDescriptor`.

        .. note::
            This method is called  during construction of the `Model`.
        """
        model_class._meta.add_field(self)
        setattr(model_class, self.name, _FieldDescriptor(self))