Enum entry expressions have the type of their enum, so it shouldn't be possible
to access static nested classes of enum entries from outside.
This fixes BlackBoxCodegenTestGenerated$CallableReference.testEnumNameMethod
#KT-2771 In Progress
ClassifierCollector now collects all enum declarations inside non-static
classes. After all declarations are done, it processes these enums: creates
a class object if it's not present, reports errors on each enum if a class
object is not allowed, and puts every enum into this class object otherwise,
recording this fact to trace.
Alexander Udalov