Fix local anonymous class name error in K2MetadataCompiler

Extract the logic of approximating to denotable class supertype
from JS/KLIB and use it in metadata compiler.

^KT-20996 In Progress

compiler/cli/src/org/jetbrains/kotlin/cli/metadata/MetadataSerializerExtension.kt

@@ -17,6 +17,7 @@
 package org.jetbrains.kotlin.cli.metadata
 
 import org.jetbrains.kotlin.metadata.builtins.BuiltInsBinaryVersion
+import org.jetbrains.kotlin.serialization.ApproximatingStringTable
 import org.jetbrains.kotlin.serialization.KotlinSerializerExtensionBase
 import org.jetbrains.kotlin.serialization.deserialization.builtins.BuiltInSerializerProtocol
 
@@ -24,4 +25,5 @@ class MetadataSerializerExtension(
     override val metadataVersion: BuiltInsBinaryVersion
 ) : KotlinSerializerExtensionBase(BuiltInSerializerProtocol) {
     override fun shouldUseTypeTable(): Boolean = true
+    override val stringTable = ApproximatingStringTable()
 }