umbrello/petaltree2uml.cpp - Add importing of enum types from Rose :

- New ClassifierListReader child class LiteralsReader furnishes
  boilerplate for converting from PetalNode to UMLEnumLiteral.
- In function umbrellify, if parsed class has some form of enum
  stereotype (such as "enum", "Enumeration", "CORBAEnum" etc) then
  - call Object_Factory::createUMLObject for type UMLObject::ot_Enum;
  - run LiteralsReader::read on the returned UMLEnum.

CCBUG: 81364