Issues with dragging and pushing vehicles over ramps

[olanti-p]

Describe the bug

Continuation of #1978.

It's impossible to grab vehicles over ramps, or maintain a grab when moving over ramp.

As a consequence:

1. It's impossible to drag a vehicle up or down a ramp
2. When pushing the vehicle up or down a ramp, the avatar lets go of it
3. It's impossible to move the vehicle if character can't access the vehicle's z-level (e.g. it was the only corridor, and the vehicle is non-boardable, so it gets permanently stuck after pushing and blocks the way)

Steps To Reproduce

1. Find a bridge
2. Tp to a bridgehead
3. Spawn shopping cart
4. Try dragging or pushing it over ramps

Expected behavior

1. When dragging vehicle over ramp, the avatar doesn't let go
2. When pushing vehicle over ramp, the avatar doesn't let go
3. It's possible to grab the vehicle that is on same ramp yet on another z-level

Screenshots

No response

Versions and configuration

Game version 22ef16d4

Additional context

Grab position tracking is already a tripoint, but the z part doesn't seem to be used.

[chaosvolt]

Recent discovery with ramps: in addition to the usually issue of a single-tile cart only working if pushed up/down the ramp and not pulled, multi-tile ones don't work very well at all.

The cannons added in https://github.com/cataclysmbnteam/Cataclysm-BN/pull/3351 are basically stuck up on the lower level, if you try to push them down they get stuck halfway through and you can't get them out without teleporting into the ramp it seems, and for good measure you seem to also need to install an extra wheel on one of the other two tiles. Pushing them back up also fails unless you have a wheel installed in the handle on the rear. I'll need to play around with it more to determine exactly what setups do and don't work just to be sure.