Better handling of "horizon" texture

[eevee]

trafficstars

Currently it's just drawn in a grid, with a hard edge. Obviously this doesn't make a lot of sense; it would be nice to have, say, a horizon of trees that partially hang over the walkable area, and perhaps don't have quite a straight line. Also that cast shadows!

Particular difficulty here is dealing with more trees within the map proper that use the same texture.