[Serialization] Reorganize module structure

plugins/kotlinx-serialization/testData/boxIr/sealedInterfaces.kt

@@ -0,0 +1,37 @@
+// IGNORE_BACKEND_FIR: JVM_IR
+// TARGET_BACKEND: JVM_IR
+
+// WITH_STDLIB
+
+package a
+
+import kotlinx.serialization.*
+
+import kotlinx.serialization.descriptors.*
+import kotlin.test.assertEquals
+
+interface I
+
+sealed interface SI
+
+@Serializable
+sealed interface SSI
+
+@Serializable
+class Holder(
+    val i: I,
+    val si: SI,
+    val ssi: SSI
+)
+
+fun SerialDescriptor.checkKind(index: Int, kind: String) {
+    assertEquals(kind, getElementDescriptor(index).kind.toString())
+}
+
+fun box(): String {
+    val desc = Holder.serializer().descriptor
+    desc.checkKind(0, "OPEN")
+    desc.checkKind(1, "OPEN")
+    desc.checkKind(2, "SEALED")
+    return "OK"
+}