Load Java enums as final classes

In case Java enum has an abstract member, it has the ACC_ABSTRACT flag
set in the bytecode. However, we should still load it with final
modality to be consistent with Kotlin enums which are always considered
final

 #KT-23426 Fixed

compiler/testData/diagnostics/tests/enum/javaEnumWithAbstractFun.txt

@@ -2,7 +2,7 @@ package
 
 public fun main(): kotlin.Unit
 
-public abstract enum class A : kotlin.Enum<A!> {
+public final enum class A : kotlin.Enum<A!> {
     enum entry ENTRY
 
     public constructor A()