[java] ClassWithOnlyPrivateConstructorsShouldBeFinal - fix FP with inner private classes #3668 * pr-3668: Compare subtypes without generics [java] ClassWithOnlyPrivateConstructorsShouldBeFinal - add test case with generics [java] ClassWithOnlyPrivateConstructorsShouldBeFinal - simplify [java] ClassWithOnlyPrivateConstructorsShouldBeFinal - consider nested [java] ClassWithOnlyPrivateConstructorsShouldBeFinal - allow non-abstract abstract classes [java] ClassWithOnlyPrivateConstructorsShouldBeFinal - exclude abstract classes