ruins_4x4_camp: Fix intermittent CI error

[hexagonrecursion]

WIP: this PR includes #55627 to (hopefully) get green CI (pray with me, if you are religious)

Summary

None

Purpose of change

CI has failed on me twice with:

ERROR : src/mapgen.cpp:2589 [virtual void jmapgen_terrain::apply(const mapgendata&, const jmapgen_int&, const jmapgen_int&, const string&) const] In nested mapgen ruins_4x4_camp in mapgen desolatebarn on desolatebarn_west, setting terrain to t_dirtfloor (from t_dirt) at (6,11) when furniture was f_rubble.  Resolve this either by removing the terrain from this mapgen, adding suitable removal commands to the mapgen, or by adding a suitable flag to the innermost mapgen: either ERASE_ALL_BEFORE_PLACING_TERRAIN if you wish terrain to replace everything previously on the tile or ALLOW_TERRAIN_UNDER_OTHER_DATA if you wish the other items to be preserved225.142 s: overmap_terrain_coverage

Describe the solution

I have looked at a couple of fixes for similar errors and found that the solution was to add ERASE_ALL_BEFORE_PLACING_TERRAIN

Testing

• TODO

1. The game loads
2. debug -> [m]ap -> [M]ap editor -> [o]vermap
3. Find desolate barn
4. Hold down "regenerate". w/o this patch you would eventually hit a debug assertion at this step

[PatrikLundell]

The solution is to add either ERASE_ALL_BEFORE_PLACING_TERRAIN or ALLOW_TERRAIN_UNDER_OTHER_DATA. The problem is to figure out which one to add, which means you have to actually understand what the usage of the blueprint is trying to achieve.
If the intention is to replace what was there before ERASE is the correct choice, while if it is to add to it ALLOW is the correct one.

It can be noted that the behavior before the introduction of the flags and the checks was NOT to remove things (except when walls are placed, in which case special code older than the flags is invoked). Thus, blindly applying ERASE to anything flagged changes the behavior, but on the other hand, most of the mapgen probably desires the new behavior...
The situation is a significant mess, and the warnings shouldn't have been introduced until after a major effort to update all map gen and base camp construction had been performed.

[hexagonrecursion]

In this case the base mapgen places rubble at random coordinates that sometimes just happen to land in the wrong place. I think erase is correct here