Stop ant tunnels stomping over other map terrain underground and removing staircases

[ghost]

Summary

SUMMARY: Bugfixes "Stop ant tunnels stomping over other map terrain underground and removing staircases"

Purpose of change

Fixes #27195

Describe the solution

As per ralreegorganons comment on linked issue, adde da check for solid rock terrain before allowing ant tunnel to be placed, this would stop it replacing map specials that need to retain their staircases.

Describe alternatives you've considered

N/A

Testing

found an intersecting subway/anthill, and the subway retained its staircase going up.

Additional context

N/A

[I-am-Erk]

so just like, fix a year-old release blocker and a bug as old as anthills in a couple hours with five lines of code, why dontcha.

[ghost]

so just like, fix a year-old release blocker and a bug as old as anthills in a couple hours with five lines of code, why dontcha.

Turns out I didnt really :P Infact I made it worse, thats what I get for working on an area I really dont understand and botching it because I thought it was a real simple fix :P

[I-am-Erk]

I saw. You monster