[Serialization] Reorganize module structure

plugins/kotlinx-serialization/testData/firMembers/serializableObject.kt

@@ -0,0 +1,15 @@
+// WITH_STDLIB
+
+import kotlinx.serialization.*
+import kotlinx.serialization.json.*
+
+@Serializable
+object FooBar
+
+fun box(): String {
+    val encoded = Json.encodeToString(FooBar.serializer(), FooBar)
+    if (encoded != "{}") return encoded
+    val decoded = Json.decodeFromString(FooBar.serializer(), encoded)
+    if (decoded !== FooBar) return "Incorrect object instance"
+    return "OK"
+}