Added support for a priority lane for entity spawning

It's now possible to have high and normal priority calls on the spawnable entities manager. This allows for events like (de)spawning and retrieving information to be executed before already queued requests, though requests cannot be reordered on the same ticket. High priority calls are executed twice per frame, while normal priority calls are called only once.

Code/Framework/AzFramework/AzFramework/Spawnable/SpawnableSystemComponent.h

@@ -28,6 +28,7 @@ namespace AzFramework
     class SpawnableSystemComponent
         : public AZ::Component
         , public AZ::TickBus::Handler
+        , public AZ::SystemTickBus::Handler
         , public AssetCatalogEventBus::Handler
         , public RootSpawnableInterface::Registrar
         , public RootSpawnableNotificationBus::Handler
@@ -58,6 +59,13 @@ namespace AzFramework
         //
 
         void OnTick(float deltaTime, AZ::ScriptTimePoint time) override;
+        int GetTickOrder() override;
+
+        //
+        // SystemTickBus
+        //
+
+        void OnSystemTick() override;
 
         //
         // AssetCatalogEventBus