Add separate overmap font, Fix framebuffer artifacts

Adds support for a separate, different-sized ASCII font for the overmap.
Now almost all map/terrain display in the game can be decoupled from the text, allowing to use readable rectangular fonts for one, and pretty square fonts for the other.

In the making of this feature, my previous attempt at fixing the framebuffer artifacts as reported in #9348 was broken on the overmap, and as a result it was folded into this feature as well, as it depends on some of the new window IDs.