Creatures check for clear line of sight
Fixes #1272
This does not work yet:

Dependent on https://github.com/dkfans/keeperfx/pull/1884
I am scoping out trying to shoot through floors. This is not a new issue.
It is caused by a bug in point_in_map_is_solid, which makes the top slab of floors non-solid. Fixing this bug exposes several complications with the battle code if there is a height difference between units (land-guardpost-lava), since units who cannot reach an enemy by foot, nor can shoot them from their current position deem it an unwinnable battle and will flee. Moving closer or to a different position is not considered.