[Serialization] Reorganize module structure

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

@@ -0,0 +1,22 @@
+// WITH_STDLIB
+
+import kotlinx.serialization.*
+import kotlinx.serialization.json.*
+
+@Serializable
+class SomeClass(val i: Int)
+
+fun box(): String {
+    val targetString = """{"i":42}"""
+    val serializer = SomeClass.Companion.serializer()
+    val descriptor = serializer.descriptor
+    if (descriptor.toString() != "SomeClass(i: kotlin.Int)") return "Incorrect SerialDescriptor.toString(): $descriptor"
+    val instance = SomeClass(42)
+    val string = Json.encodeToString(serializer, instance)
+    if (string != targetString) return "Incorrect serialization result: expected $targetString, got $string"
+    val instance2 = Json.decodeFromString(serializer, string)
+    if (instance2.i != instance.i) return "Incorrect deserialization result: expected ${instance.i}, got ${instance2.i}"
+    return "OK"
+}
+
+