WIP: Bugfix: Crushing polyobjects being unable to squish

UNCERTAIN about second commit, discuss if it should be reverted to first commit before merging

changed target branch from master to next

Hm, this might not work if your sector isn't the same as that of the poly's "front" sector, as I explained on Discord. I suggested using the blockmap instead to find objects to squish, in a similar way to what P_CheckSector does?

(except not using touching thinglist but instead blockmap, I mean)

mentioned in merge request !426 (merged)

I cherry-picked the first commit via !426 (merged)

(re merge conflict, probably just need to merge the latest next to this branch, which should show no changes.)

marked as a Work In Progress

Setting to WIP until I have something I'm happier with

mentioned in merge request !505 (merged)

closed