Reserve paths before adding forests or semi-decorative debris

[ashleynewson]

Minimal paths connecting playable areas could be identified by shrinking playable space until separate non-playable spaces meet.

Minimal paths could then be re-expanded by some amount to create a reserved space that semi-decorative obstructions must not be placed in.

The shrinking process could be biased with 2d noise to avoid unnatural looking cut-outs right in the middle of playable space.

[ashleynewson]

This can borrow the Voronoi processing logic from the road generation work.

[ashleynewson]

Done