Allow custom sprites for corpses.

[OzoneH3]

Summary

SUMMARY: Features "Allow custom sprites for corpses."

Purpose of change

Fixes #24655 (@SomeDeadGuy)

Describe the solution

This allows to add corpse specific sprites without adding a
dedicated corpse item to the game since corpses are just
a generic corpse with an mtype attached.
Will fallback to the normal corpse sprite if no custom one is found.

Additional context

To add a custom sprite just add corpse_ in front of the monster id.

{
    "id": "corpse_mon_zombie_rot",
    "fg": 1848
},