Cache TargetablePositions in Actor

To speed up Target.Positions.

OpenRA.Mods.Common/Traits/HitShape.cs

@@ -73,6 +73,8 @@ namespace OpenRA.Mods.Common.Traits
 			base.Created(self);
 		}
 
+		bool ITargetablePositions.AlwaysEnabled { get { return Info.RequiresCondition == null; } }
+
 		IEnumerable<WPos> ITargetablePositions.TargetablePositions(Actor self)
 		{
 			if (IsTraitDisabled)

OpenRA.Mods.Common/TraitsInterfaces.cs

@@ -334,8 +334,6 @@ namespace OpenRA.Mods.Common.Traits
 		IEnumerable<object> ActorPreviewInits(ActorInfo ai, ActorPreviewType type);
 	}
 
-	public interface IMoveInfo : ITraitInfoInterface { }
-
 	public interface IMove
 	{
 		Activity MoveTo(CPos cell, int nearEnough);