AI Reachable system

[metalgearsloth]

Like the first third of a hierarchical pathfinder. This system prevents AI from trying to pathfind into areas they can't get to.
Previously it was Grid -> Chunks -> Nodes
Now there's also Grid -> Chunks -> Regions -> Nodes (where regions slot themselves into the existing system).

The reason for this is it's faster to traverse regions rather than nodes because regions are made up of tiles. My first attempt I tried just using the BFS pathfinder on nearby tiles so the AI could tell whether it could access a particular node but even with caching it was too slow.

Regions are created from areas of homogenous pathfinding nodes (i.e. all the same collision mask, all space etc.) within a single chunk, though currently walls are ignored for now.
There's probably a better data structure to use for regions but even this version gives a significant speedup for the AI checking whether it can access an entity or not. Plus some of the chunk update stuff is grossly inefficient.
AI can also re-use existing cached reachable regions as well.

Adds 2 commands for debugging:

• pathfinder regions shows every region in different colours
• pathfinder regioncache will show when the AI is checking for accessibility (green means cache is updated, blue means existing cache hit).

I also re-wrote the wander behavior so the idle AI should be SIGNIFICANTLY faster and not spamming out paths to places it can't get to twice a second.

For reference I know Factorio and Rimworld have their own hierarchical systems and this one falls more on the Rimworld side (though rooms aren't generated and the chunk update is inefficient).