FIR: add getClassifierNames for FirScope

compiler/fir/java/src/org/jetbrains/kotlin/fir/java/scopes/JavaClassUseSiteMemberScope.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -49,6 +49,10 @@ class JavaClassUseSiteMemberScope(
         return declaredMemberScope.getCallableNames() + superTypesScope.getCallableNames()
     }
 
+    override fun getClassifierNames(): Set<Name> {
+        return declaredMemberScope.getClassifierNames() + superTypesScope.getClassifierNames()
+    }
+
     private fun generateAccessorSymbol(
         functionSymbol: FirFunctionSymbol<*>,
         syntheticPropertyName: Name,