In a fdl.Config for a dataclass, when accessing a field that uses a default_factory, populate a child Config (if not already present) wrapping the default_factory call, rather than raising a "Can't get default value for dataclass field ... since it uses a default_factory" error.

In a fdl.Config for a dataclass, when accessing a field that uses a default_factory, populate a child Config (if not already present) wrapping the default_factory call, rather than raising a "Can't get default value for dataclass field ... since it uses a default_factory" error. #1810