[Gradle, JS] Add appendix for archive in case of mixed mode

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/KotlinJsTargetConfigurator.kt

@@ -5,6 +5,7 @@
 
 package org.jetbrains.kotlin.gradle.targets.js
 
+import org.gradle.api.tasks.bundling.Jar
 import org.gradle.language.base.plugins.LifecycleBasePlugin
 import org.jetbrains.kotlin.gradle.dsl.kotlinExtension
 import org.jetbrains.kotlin.gradle.plugin.Kotlin2JsSourceSetProcessor
@@ -12,6 +13,7 @@ import org.jetbrains.kotlin.gradle.plugin.KotlinOnlyTargetConfigurator
 import org.jetbrains.kotlin.gradle.plugin.KotlinSourceSetProcessor
 import org.jetbrains.kotlin.gradle.plugin.KotlinTargetWithTestsConfigurator
 import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinJsCompilation
+import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinOnlyTarget
 import org.jetbrains.kotlin.gradle.plugin.mpp.defaultSourceSetName
 import org.jetbrains.kotlin.gradle.targets.js.ir.KotlinJsIrTargetConfigurator
 import org.jetbrains.kotlin.gradle.tasks.KotlinTasksProvider
@@ -90,6 +92,15 @@ open class KotlinJsTargetConfigurator(kotlinPluginVersion: String, val irConfigu
         }
     }
 
+    override fun createJarTasks(target: KotlinOnlyTarget<KotlinJsCompilation>) {
+        super.createJarTasks(target)
+        val jar = target.project.tasks.getByName(target.artifactsTaskName) as Jar
+
+        if (irConfigurator != null) {
+            jar.archiveAppendix.set("legacyJs")
+        }
+    }
+
     override fun configureCompilations(target: KotlinJsTarget) {
         super.configureCompilations(target)