- when building a topsorted hierarchy, consider not only edges to the class'
superclasses, but also from inner/nested classes to their container. This
effectively means that a class cannot inherit from its nested class. Similar
cases (see the tests) are disallowed in Java.
- filter classes by their presence in TopDownAnalysisContext, not by being a
MutableClassDescriptor (otherwise analysis for local classes ends up trying
to do something with outer superclasses)
- delete outdated comment: topsort is needed not only for better diagnostics,
but also for correct order of fake overrides construction
Andrey Breslav