Debug note on overmap when mutable placement fails

[jbytheway]

Summary

None

Purpose of change

When mutable overmap special placement fails, it may not be immediately obvious why or where the problem is.

Describe the solution

When placement fails for a mutable overmap special, add a note to the overmap with some details to assist debugging.

Describe alternatives you've considered

Adding more stuff, like notes with the placement order for every OMT.

Using a debug terrain type instead of a note.

Testing

Adjusted the anthill to cause spawn failures. Looked at the resulting notes.

Additional context