Introduce MemberScope::classifierNames and some implementations

It aims to help with further optimizations

core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/MetadataPackageFragmentProvider.kt

@@ -107,6 +107,7 @@ class MetadataPackageFragment(
         ) {
             override fun hasClass(name: Name): Boolean = hasTopLevelClass(name)
             override fun definitelyDoesNotContainName(name: Name) = false
+            override fun getClassifierNames(): Set<Name>? = null
         })
 
         return ChainedMemberScope.create("Metadata scope", scopes)

core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/descriptors/DeserializedMemberScope.kt

@@ -76,6 +76,7 @@ abstract class DeserializedMemberScope protected constructor(
 
     override fun getFunctionNames() = functionNamesLazy
     override fun getVariableNames() = variableNamesLazy
+    override fun getClassifierNames(): Set<Name>? = classNames + typeAliasNames
 
     private inline fun <M : MessageLite> Collection<M>.groupByName(
             getNameIndex: (M) -> Int