Add a IAutoSelctionSizeInfo trait interface

OpenRA.Game/Traits/TraitsInterfaces.cs

@@ -95,6 +95,8 @@ namespace OpenRA.Traits
 	public interface ITick { void Tick(Actor self); }
 	public interface ITickRender { void TickRender(WorldRenderer wr, Actor self); }
 	public interface IRender { IEnumerable<IRenderable> Render(Actor self, WorldRenderer wr); }
+
+	public interface IAutoSelectionSizeInfo : ITraitInfoInterface { }
 	public interface IAutoSelectionSize { int2 SelectionSize(Actor self); }
 
 	public interface IIssueOrder