[KxSerialization] Fix NPE if sealed class has self-referencing property

Fixes Kotlin/kotlinx.serialization#2294

If the serializable class contains itself as a 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.

To avoid this the serialization class should not cache its own serializer as a child.

Merge-request: KT-MR-10019
Merged-by: Sergey Shanshin <Sergey.Shanshin@jetbrains.com>

plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirLightTreeBlackBoxTestGenerated.java

@@ -33,6 +33,12 @@ public class SerializationFirLightTreeBlackBoxTestGenerated extends AbstractSeri
             runTest("plugins/kotlinx-serialization/testData/boxIr/annotationsOnFile.kt");
         }
 
+        @Test
+        @TestMetadata("caching.kt")
+        public void testCaching() throws Exception {
+            runTest("plugins/kotlinx-serialization/testData/boxIr/caching.kt");
+        }
+
         @Test
         @TestMetadata("classSerializerAsObject.kt")
         public void testClassSerializerAsObject() throws Exception {

plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationIrBoxTestGenerated.java

@@ -31,6 +31,12 @@ public class SerializationIrBoxTestGenerated extends AbstractSerializationIrBoxT
         runTest("plugins/kotlinx-serialization/testData/boxIr/annotationsOnFile.kt");
     }
 
+    @Test
+    @TestMetadata("caching.kt")
+    public void testCaching() throws Exception {
+        runTest("plugins/kotlinx-serialization/testData/boxIr/caching.kt");
+    }
+
     @Test
     @TestMetadata("classSerializerAsObject.kt")
     public void testClassSerializerAsObject() throws Exception {