WIP Placement handler

[tomjn]

Implements a building placement algorithm:

• optimised for spreading cpu load across multiple frames
• pluggable placement test functions
• configurable search increment and radius
• runs in a square spiral pattern moving outwards
• operates on a job system with async requests, give it a job and it'll call a function you pass on completion/failure so that you can do something with the result

Some features still need fully testing, some are partially implemented at the time of writing

[tomjn]

Current testing showed that units tend to stop doing things, though no debugging has been done to determine why just yet. Probably because not enough positions are being checked per game frame. Until the timing code is finished it's doing a set number of iterations rather than using time budgets as intended, so I was conservative, maybe too conservative about it

[pandaro]

interesting

[tomjn]

Recent tests and modifications added basic spacing support, the algorithm is now competent enough to be used as a replacement

Additionally, changes were made to allow this widget to be used to debug it:

https://gist.github.com/tomjn/01ada053704d523502729ebdc23299a1

[tomjn]

I would also note that the latest commits made changes that aren't compatible with native Shard. I'm fine with this