[FIR] Properly implement serializer extension for klib compilation

^KT-57654 Fixed

js/js.translator/testData/box/inlineMultiModule/extensionLambda.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_K2: JS_IR
 // EXPECTED_REACHABLE_NODES: 1285
 // MODULE: lib
 // FILE: lib.kt
@@ -25,4 +24,4 @@ fun box(): String {
     assertEquals(6, test(A(2), 3))
 
     return "OK"
-}
+}