Refactor AutoTarget scan and GPS interaction, and cache trait lookup for a slight performance boost

OpenRA.Game/Traits/TraitsInterfaces.cs

@@ -112,6 +112,8 @@ namespace OpenRA.Traits
 	}
 
 	public interface IVisibilityModifier { bool IsVisible(Actor self, Player byPlayer); }
+	public interface IFogVisibilityModifier { bool HasFogVisibility(Player byPlayer); }
+
 	public interface IRadarColorModifier { Color RadarColorOverride(Actor self); }
 
 	public interface IOccupySpaceInfo { }