Overmap path fixes

[eltank]

Summary

Bugfixes "Overmap pathing: allow subway, disallow rock"

Purpose of change

This is a follow-up to #50637. I was too focused on overland navigation and didn't consider underground.

Describe the solution

Don't allow pathing through solid rock / earth.
Allow vehicles to drive in the subway tunnels.

Describe alternatives you've considered

Special case burrowing mutants to allow pathing through rock? Seems like too much hassle, and burrowing is hard work so you probably want to avoid it anyway.

Testing

subway_biking.mp4

Additional context

Seeing a lot more monsters in the subway tunnels than I ever remember seeing.

[actual-nh]

Re subway critters: See #48772.

[eltank]

Re subway critters: See #48772.

Thanks, now I see that at z=-4 there's yet more new terrain I need to handle. [Done]

[eltank]

Found an unrelated bug while testing this: #50696

[Venera3]

Do you think you can hook it up to handle rail vehicles? Turning's pretty wonky at the moment, and some assistance in gauging speeds/distance would be helpful.

[eltank]

Do you think you can hook it up to handle rail vehicles? Turning's pretty wonky at the moment, and some assistance in gauging speeds/distance would be helpful.

I've added your feature request to the list (#49455). A prerequisite for autodriving rail vehicles is keeping track of where the wheels are. I'm planning on doing that anyway, mostly because I hate driving over any "loot piles" that I made. But there's an additional complication for rail vehicles, which is that when the track bends they temporarily go off-track with some of their wheels. Predicting how they're going to take a turn seems rather difficult at the moment. Another problem with draisines is that half the time you need to run them in reverse, flipping them around is not an option -- and autodrive does not support reverse driving yet.
So... it's going to take a while.