LC: rework modality of enum class

It is abstract if it has abstract member.
It is final if it doesn't have enum entries that need subclass.
Otherwise, it is open (i.e., no modifier)

^KT-57567 Fixed

compiler/testData/asJava/lightClasses/lightClassByPsi/enums.fir.java

@@ -86,7 +86,7 @@ static final class PLUS /* IntArithmetics.PLUS*/ extends IntArithmetics {
   public int apply(int, int);//  apply(int, int)
 }
 
-public enum ProtocolState /* ProtocolState*/ {
+public abstract enum ProtocolState /* ProtocolState*/ {
   WAITING {
    WAITING();//  .ctor()