Export deserialization constructor from JS module

Fixes https://github.com/Kotlin/kotlinx.serialization/issues/443

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/js/SerializableJsTranslator.kt

@@ -121,6 +121,7 @@ class SerializableJsTranslator(
 
         f.name = context.getInnerNameForDescriptor(constructorDescriptor)
         context.addDeclarationStatement(f.makeStmt())
+        context.export(constructorDescriptor)
     }
 
     private fun JsBlockBuilder.generateSuperNonSerializableCall(superClass: ClassDescriptor, thisParameter: JsExpression) {
@@ -139,7 +140,7 @@ class SerializableJsTranslator(
         thisParameter: JsExpression,
         propertiesStart: Int
     ): Int {
-        val constrDesc = KSerializerDescriptorResolver.createLoadConstructorDescriptor(superClass, context.bindingContext())
+        val constrDesc = superClass.constructors.single(ClassConstructorDescriptor::isSerializationCtor)
         val constrRef = context.getInnerNameForDescriptor(constrDesc).makeRef()
         val superProperties = bindingContext.serializablePropertiesFor(superClass).serializableProperties
         val superSlots = superProperties.bitMaskSlotCount()

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/resolve/SearchUtils.kt

@@ -13,13 +13,21 @@ import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.psi.ValueArgument
 import org.jetbrains.kotlin.resolve.constants.KClassValue
+import org.jetbrains.kotlin.resolve.descriptorUtil.classId
 import org.jetbrains.kotlin.resolve.descriptorUtil.module
 import org.jetbrains.kotlin.resolve.lazy.descriptors.LazyAnnotationDescriptor
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.KotlinTypeFactory
 
-internal fun ClassConstructorDescriptor.isSerializationCtor(): Boolean =
-    kind == CallableMemberDescriptor.Kind.SYNTHESIZED && valueParameters.lastOrNull()?.name == SerialEntityNames.dummyParamName
+internal fun ClassConstructorDescriptor.isSerializationCtor(): Boolean {
+    /*kind == CallableMemberDescriptor.Kind.SYNTHESIZED does not work because DeserializedClassConstructorDescriptor loses its kind*/
+    return valueParameters.lastOrNull()?.run {
+        name == SerialEntityNames.dummyParamName && type.constructor.declarationDescriptor?.classId == ClassId(
+            SerializationPackages.packageFqName,
+            SerialEntityNames.SERIAL_CTOR_MARKER_NAME
+        )
+    } == true
+}
 
 // finds constructor (KSerializer<T0>, KSerializer<T1>...) on a KSerializer<T<T0, T1...>>
 internal fun findSerializerConstructorForTypeArgumentsSerializers(