Add isData() to ClassDescriptor

compiler/backend/src/org/jetbrains/kotlin/codegen/MutableClassDescriptor.java

@@ -100,6 +100,11 @@ public class MutableClassDescriptor extends ClassDescriptorBase implements Class
         return isInner;
     }
 
+    @Override
+    public boolean isData() {
+        return false;
+    }
+
     @Override
     public boolean isCompanionObject() {
         return false;