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/tests/org/jetbrains/kotlin/asJava/KotlinLightClassStructureTest.java

@@ -75,7 +75,7 @@ public abstract class KotlinLightClassStructureTest extends KotlinAsJavaTestBase
         }
 
         public void testEnum() {
-            checkModifiers("test.Enum", PUBLIC, ENUM);
+            checkModifiers("test.Enum", PUBLIC, FINAL, ENUM);
         }
 
         public void testTrait() {