[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/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JSCompilerArguments.kt

@@ -268,6 +268,9 @@ class K2JSCompilerArguments : CommonCompilerArguments() {
             if (!isIrBackendEnabled()) {
                 this[LanguageFeature.JsAllowInvalidCharsIdentifiersEscaping] = LanguageFeature.State.DISABLED
             }
+            if (isIrBackendEnabled()) {
+                this[LanguageFeature.JsAllowValueClassesInExternals] = LanguageFeature.State.ENABLED
+            }
         }
     }
 }