[FIR Serialization] Fix serialization of generated nested classifiers

^KT-55759 Fixed

plugins/kotlinx-serialization/testData/boxIr/generatedClassifiersViaLibraryDependency.kt

@@ -0,0 +1,23 @@
+// ISSUE: KT-55759
+// TARGET_BACKEND: JVM_IR
+// WITH_STDLIB
+
+// MODULE: lib
+// TARGET_PLATFORM: JVM
+// FILE: lib.kt
+
+import kotlinx.serialization.*
+
+@Serializable
+class Test
+
+// MODULE: jvm(lib)()()
+// TARGET_PLATFORM: JVM
+// FILE: main.kt
+
+import kotlinx.serialization.*
+import kotlinx.serialization.descriptors.*
+
+fun box(): String {
+    return if (Test.serializer().descriptor.toString() == "Test()") "OK" else "FAIL"
+}