- Add utilities to add new attribute to ConeAttributes
- Get rid of FlexibleNullability attribute (it can be easily inferred
for any flexible type at any moment)
- Fix determining of EnhancedNullability attribute
Really, this commit implements early J2K mapping for all Java types.
It's questionable and probably wrong at least for super-types,
because, for example, we cannot resolve spliterator() in classes
derived from java.lang.Iterable