Consider adding pathfinding tests

[lynxlynxlynx]

Fixing pathfinding bugs is quite tricky, but the core functions like FindPath are isolated and we could perhaps at least test for their correctness to make development easier. Static things like avoiding teleporting and pathing through walls, detecting overall path changes, should a bump occur etc.
I don't know if our test rig could easily handle it, but we'd also need to craft or reuse searchmap data.

• straight horizontal path
• straight diagonal path (at some odd angle that doesn't match any of the 16 orientations)
• path around a square obstacle (just another determinism check)
• circle size 2 actor passing through gap of 1 tile
• not tunnelling to a target over a thin wall

Some ideas from another bug:

• moving actor around party members standing in a square (open and narrow space)
• moving party through a narrow corridor
• moving party through a narrow intersecting corridors (like in the area I tested in
• Pathfinding in narrow corridors is suboptimal Pathfinding in narrow corridors is suboptimal  #1825)
• moving around actors with larger circles - I have no idea where to find them

Then also repeat some of these with bigger circle sizes and actors in the way (moving or not).