A non-abstract super-declaration is allowed to stand as 'an implementation' of
a fake override only if its visibility is not less than visibilities of all
other super-declarations
#KT-2491 Fixed
Some corner cases still remain: KotlinSignature, propagation, deserialized
delegates to Java interfaces
#KT-1239 Obsolete
#KT-1924 In Progress
#KT-2081 Fixed