Minor, move diagnostic tests for class objects
Report INVISIBLE_MEMBER on private class object usage
Report upper bounds violation for objects, not only classes
Class objects also can have delegated members
Disable "UseOfSystemOutOrSystemErr" inspection in tests
Minor refactorings in codegen tests

Unindent code, get rid of warnings, etc.
Minor, add error message & Override
Minor, use headless mode in BuiltInsSerializer
Minor, inline method
Extract SpecialNames utility class
Extract SpecialNames.isClassObjectName
Add a test on extension function to object
Minor, rename method
Minor, move enum diagnostic tests, add another test