[KxSerialization] Fix NPE if sealed class has self-referencing in generic parameter

Fixes #KT-58918

If the serializable class contains itself as a generic parameter of the property, and its serializer is not an object (for example, for a sealed class), in this case there is a race in the initialization of the serializer and child serializers.

Merge-request: KT-MR-10363
Merged-by: Sergey Shanshin <Sergey.Shanshin@jetbrains.com>

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

@@ -17,6 +17,20 @@ open class Open(val p: Open? = null)
 @Serializable
 abstract class Abstract(val p: Abstract? = null)
 
+@Serializable
+class GenericHolder<T> {
+    var value: T? = null
+}
+
+@Serializable
+sealed class SealedGeneric {
+    var holder = GenericHolder<SealedGeneric>()
+}
+
+@Serializable
+sealed class SealedListGeneric {
+    var holder = GenericHolder<GenericHolder<List<SealedListGeneric>>>()
+}
 
 fun box(): String {
     // A correctly cached class must be initialized correctly in order to exclude cyclic nesting of caches
@@ -24,6 +38,8 @@ fun box(): String {
     Sealed.serializer()
     Open.serializer()
     Abstract.serializer()
+    SealedGeneric.serializer()
+    SealedListGeneric.serializer()
 
     return "OK"
 }