Improve creation of generalization with parent provided as string:

umbrello/codeimport/import_utils.cpp
- In function createGeneralization(UMLClassifier*, const QString&),
  if parentName contains a scope separator then
  - split the qualified name into its parts using the scope separator
    as the divider;
  - save the last element of the split list as className and pop that
    element off the list;
  - declare local variables `parent' and `current' of type UMLPackage*;
  - iterate over the list and create each package path segment using
    the 7 argument form of Import_Utils::createUMLObject();
  - on iterating, use the variables `parent' and `current' to track
    the UML packages created, such that the path segments are assembled
    with the proper hierarchical nesting;
  - after the package creation loop, create the className object using
    the 7 argument form of Import_Utils::createUMLObject() and using
    `parent' as the parent package.

BUG:416178