Move spawning collections of EntitySpawnEntry out of StorageSystem, make Butcherable use it (#7305)

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>

Content.Server/Storage/Components/StorageFillComponent.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using Content.Server.Storage.EntitySystems;
+using Content.Shared.Storage;
 using Robust.Shared.Analyzers;
 using Robust.Shared.GameObjects;
 using Robust.Shared.Serialization.Manager.Attributes;