KPM: add module name to directory names in the sources JAR

For example, it will now be `common` -> `commonMain`, so that the
behavior emulates the sources JARs built by the stable MPP plugin

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/pm20/KotlinSourceArchiveTaskConfigurator.kt

@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.gradle.plugin.mpp.pm20
 
 import org.gradle.api.tasks.TaskProvider
+import org.jetbrains.kotlin.gradle.plugin.mpp.pm20.util.unambiguousNameInProject
 import org.jetbrains.kotlin.gradle.plugin.mpp.sourcesJarTaskNamed
 
 interface KotlinSourceArchiveTaskConfigurator<in T : KotlinGradleVariant> {
@@ -19,7 +20,7 @@ object DefaultKotlinSourceArchiveTaskConfigurator : KotlinSourceArchiveTaskConfi
             project = variant.project,
             sourceSets = lazy {
                 FragmentSourcesProvider().getSourcesFromRefinesClosureAsMap(variant)
-                    .entries.associate { it.key.fragmentName to it.value.get() }
+                    .entries.associate { it.key.unambiguousNameInProject to it.value.get() }
             },
             artifactNameAppendix = variant.name
         )