Add support to export nested container entities. Resolves missing parents in spawnables

Code/Framework/AzToolsFramework/AzToolsFramework/Prefab/Instance/Instance.cpp

@@ -187,13 +187,14 @@ namespace AzToolsFramework
             return removedEntity;
         }
 
-        void Instance::DetachNestedEntities(const AZStd::function<void(AZStd::unique_ptr<AZ::Entity>)>& callback)
+        void Instance::DetachAllEntitiesInHierarchy(const AZStd::function<void(AZStd::unique_ptr<AZ::Entity>)>& callback)
         {
+            callback(AZStd::move(DetachContainerEntity()));
             DetachEntities(callback);
 
             for (const auto& [instanceAlias, instance] : m_nestedInstances)
             {
-                instance->DetachNestedEntities(callback);
+                instance->DetachAllEntitiesInHierarchy(callback);
             }
         }
 

Code/Framework/AzToolsFramework/AzToolsFramework/Prefab/Instance/Instance.h

@@ -87,7 +87,14 @@ namespace AzToolsFramework
             bool AddEntity(AZ::Entity& entity, EntityAlias entityAlias);
             AZStd::unique_ptr<AZ::Entity> DetachEntity(const AZ::EntityId& entityId);
             void DetachEntities(const AZStd::function<void(AZStd::unique_ptr<AZ::Entity>)>& callback);
-            void DetachNestedEntities(const AZStd::function<void(AZStd::unique_ptr<AZ::Entity>)>& callback);
+
+            /**
+            * Detaches all entities in the instance hierarchy, including; all direct and nested entities, all container entities.
+            * Note that without container entities the hierarchy that remains cannot be used further without restoring new ones
+            * @param callback A user provided callback that can be used to capture ownership and manipulate the detached entities.
+            */
+            void DetachAllEntitiesInHierarchy(const AZStd::function<void(AZStd::unique_ptr<AZ::Entity>)>& callback);
+
             void RemoveNestedEntities(const AZStd::function<bool(const AZStd::unique_ptr<AZ::Entity>&)>& filter);
 
             void Reset();

Code/Framework/AzToolsFramework/AzToolsFramework/Prefab/Spawnable/SpawnableUtils.cpp

@@ -38,11 +38,7 @@ namespace AzToolsFramework::Prefab::SpawnableUtils
                                                                               // going to be used to create clones of the entities.
         {
             AzFramework::Spawnable::EntityList& entities = spawnable.GetEntities();
-            if (instance.HasContainerEntity())
+            instance.DetachAllEntitiesInHierarchy(
-            {
-                entities.emplace_back(AZStd::move(instance.DetachContainerEntity()));
-            }
-            instance.DetachNestedEntities(
                 [&entities](AZStd::unique_ptr<AZ::Entity> entity)
                 {
                     entities.emplace_back(AZStd::move(entity));