Replaced deprecated methods and calls

[dmatej]

• Factory renamed to ServantFactory
  • name based on javadoc
  • Factory caused compilation error because it is a keyword
• CodegenProxyCreator.create removed
  • deprecated, because it called deprecated PFL methods which did not work on JDK17+
• IDLLeadingUnderscoresTest - removed test for _() method name
  • Forbidden in JDK21+
  • See JEP 443
• TestCodegenProxyCreator, Sample
  • using different method than the deprecated one

Merging

• Should be merged after #189