Towing in reverse works incorrectly

When towing in reverse, the towed vehicle remains in place as the towing vehicle backs away, and closes in with the towing vehicle once the latter starts moving forward.

# Steps To Reproduce

1. Spawn two vehicles and a tow cable (reproduced using cube vans).
2. Position the towing vehicle behind the towed vehicle.
3. Connect the vehicles with the tow cable. Attach the tow cable to the front of the rear (towing) vehicle, then to the rear of the front (towed) vehicle.
4. Start the towing vehicle and accelerate in reverse. Observe the towed vehicle remaining in place.
5. Stop the towing vehicle and accelerate it forward. Observe the towed vehicle accelerating towards the towing vehicle.

# Expected behavior

Towing force applied to the towed vehicle should be directed according to the towing vehicle's motion relative to the towed vehicle, not based on the towing vehicle's speed value.

# Versions and configuration

- OS: Windows
- OS Version: 10.0 2004
- Game Version: 12fcd38 [64-bit]
- Graphics Version: Tiles
- Game Language: System language []
- Mods loaded: [
Dark Days Ahead [dda],
Disable NPC Needs [no_npc_food],
Aftershock [aftershock]
]

# Additional context

Possibly related to #46822.

Reproduce the issue with two cube vans and a tow cable, then review the related issue #46822 and locate the towing force calculation. Compare reverse and forward movement against the expected relative-motion behavior; done means the towed vehicle follows correctly in both directions.

Written by the indexing model from the issue text.