[stdlib-mpp] Fix artifact classifiers for dist

KT-56106

libraries/stdlib/build.gradle.kts

@@ -459,9 +459,16 @@ kotlin {
 }
 
 tasks {
+    val metadataJar by existing(Jar::class) {
+        archiveAppendix.set("metadata")
+    }
+    val sourcesJar by existing(Jar::class) {
+        archiveAppendix.set("metadata")
+    }
     val jvmJar by existing(Jar::class) {
         dependsOn(configurationBuiltins)
         duplicatesStrategy = DuplicatesStrategy.FAIL
+        archiveAppendix.set(null as String?)
         manifestAttributes(manifest, "Main", multiRelease = true)
         manifest.attributes(mapOf("Implementation-Title" to "kotlin-stdlib"))
         from { zipTree(configurationBuiltins.singleFile) }
@@ -472,6 +479,7 @@ tasks {
 
     val jvmSourcesJar by existing(Jar::class) {
         duplicatesStrategy = DuplicatesStrategy.FAIL
+        archiveAppendix.set(null as String?)
         into("jvmMain") {
             from("${rootDir}/core/builtins/native")
             from(kotlin.sourceSets["jvmMainJdk7"].kotlin) {