[JS IR] Allow value classes in external decls

Instances of value classes are passed unboxed, unless the instance is
nullable _and_ the value class wraps another nullable value.

#KT-43224 Fixed

compiler/test-infrastructure/tests/org/jetbrains/kotlin/test/builders/LanguageVersionSettingsBuilder.kt

@@ -88,6 +88,10 @@ class LanguageVersionSettingsBuilder {
             }
         }
 
+        if (targetBackend?.isIR == true) {
+            specificFeatures[LanguageFeature.JsAllowValueClassesInExternals] = LanguageFeature.State.ENABLED
+        }
+
         directives[LanguageSettingsDirectives.LANGUAGE].forEach { parseLanguageFeature(it) }
     }