Use .fullyExpandedType to get serializable annotation from inside typealias

to correctly handle 'global customization via typealias' feature
in K2 serialization plugin.

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

@@ -0,0 +1,44 @@
+// TARGET_BACKEND: JVM_IR
+
+// WITH_STDLIB
+
+import kotlinx.serialization.*
+import kotlinx.serialization.json.*
+import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.encoding.*
+import java.util.Date
+
+class NotSerializable(val i: Int)
+
+object SerializerB : KSerializer<NotSerializable> {
+    override val descriptor: SerialDescriptor
+        get() = PrimitiveSerialDescriptor("SerializerB", PrimitiveKind.STRING)
+
+    override fun serialize(encoder: Encoder, value: NotSerializable) = TODO()
+
+    override fun deserialize(decoder: Decoder): NotSerializable = TODO()
+}
+
+object DateSer : KSerializer<Date> {
+    override val descriptor = PrimitiveSerialDescriptor("DateSer", PrimitiveKind.DOUBLE)
+
+    override fun deserialize(decoder: Decoder): Date = TODO()
+
+    override fun serialize(encoder: Encoder, value: Date) = TODO()
+}
+
+typealias S = @Serializable(SerializerB::class) NotSerializable
+typealias BS = @Serializable(DateSer::class) Date
+
+@Serializable
+class Foo(
+    val s: S,
+    val bs: BS,
+    val list: List<BS>
+)
+
+fun box(): String {
+    val list = Foo.serializer().descriptor.elementDescriptors.map { it.serialName }.toList()
+    if (list != listOf("SerializerB", "DateSer", "kotlin.collections.ArrayList")) return list.toString()
+    return "OK"
+}