Add debug menu item for spawning nested mapgen

[ralreegorganon]

Summary

SUMMARY: Infrastructure "Add debug menu item for spawning nested mapgen"

Purpose of change

Makes it easier to develop and test nested mapgen by allowing them to be spawned from the debug menu.

Describe the solution

Add a new entry to the debug menu that lists all of the nested mapgens and allow selecting one, plus a target location to spawn it. Then load a map for that area and run the nested mapgen on it. Note that this code will get cleaner once we refactor all of mapgen to support multi-z-level and multi-omt mapgen, but for now nested mapgen can only target a single omt (and thus a single z-level), so to ensure this works we basically load a larger slice of map with a single z-level to run the nested mapgen on because the user selected location won't necessarily align to the omt grid and the nesting requires a single z-level.

Testing

Loaded the game and spawned a variety of nested mapgens (with things like NPCs and vehicles in addition to standard terrain and furniture) on various z-levels.

Additional context

[ashGlaw]

Very interesting. What’s the expected use case?

[anothersimulacrum]

People testing nested maps.