[Serialization] Reorganize module structure

plugins/kotlinx-serialization/testData/diagnostics/LazyRecursionBug.kt

@@ -0,0 +1,10 @@
+// This test enshures that analysis ends up without compiler exceptions
+// !DIAGNOSTICS: -OPT_IN_USAGE
+
+import kotlinx.serialization.*
+
+@Serializable
+class Digest() {
+    @Serializer(forClass = Digest::class)
+    companion object : KSerializer<Digest> {}
+}