MPP: Implement directory selection UI supporting non-JVM roots

#KT-27291 Fixed
 #KT-26696 Fixed

Original commit: 839d936918

jps/jps-common/src/org/jetbrains/kotlin/config/KotlinSourceRootType.kt

@@ -15,5 +15,9 @@ sealed class KotlinSourceRootType : JpsElementTypeBase<JavaSourceRootProperties>
     object TestSource : KotlinSourceRootType()
 
     override fun createDefaultProperties() = JpsJavaExtensionService.getInstance().createSourceRootProperties("")
+
+    companion object {
+        val ALL_SOURCES = setOf(Source, TestSource)
+    }
 }