Make map::add_spawn() accept a tripoint instead of a point

[kevingranade]

Summary

SUMMARY: Bugfixes "Fix monsters spawning on the player's level when intended for other levels."

Purpose of change

Fixes #36346
Spawn points placed by fields would sometimes appear on the player's level instead of the level the field was on. Specifically this affected tears in reality. From examining the code it looks like this could occur elsewhere as well, such as when an animal live birth occurred underground.

Describe the solution

Make map::add_spawn() accept a tripoint instead of a point, and update all of it's callers to supply an appropriate tripoint.

Testing

Locate an underground area with open ground over it, and ideally an upper building level that matches.
Place a tear in reality in various locations, place yourself above or below it, and wait for monsters to appear.
Monsters should appear on the level with the field, not the level with the player.