Allow egg hunt for arenas and fields

[kimden]

Description

Currently egg hunts seem to work only on tracks, that is, maps with drivelines. But the goal of exploring the map doesn't depend on whether there's driveline or navmesh, and to me it seems like the only thing driveline affects is rescuing. Looking at #605, #3390, rescuing to a driveline is far from perfect, and rescuing to navmesh might even be better.

I even think that for the purposes of Egg Hunt, the quads of driveline could be considered a special type of navmesh, with the same type of rescue.

I added an egg hunt to Emerald Arena if you need an arena for testing.

Steps to reproduce

Configuration