Add ability to waypoints to deny pathing through them depending on what's on the "front" of a train

An ability I'd like to see is waypoints being able to filter trains that can pathfind through them based on what's on the "leading end" of a train. The rationale being this can prevent trains from heading onto the mainline backwards, as cargo wagons would be leading, or even filter based on which direction the leading engine is facing, or what type of locomotive is on the leading end. Can pair this with the "can't path to next station" orders to send trains through a wye to turn around, but only on when necessary.