Relic spawns inside forest

[Salesome]

In team games, I noticed that sometimes, relics spawn inside forests, i.e. inside trees where they are trapped.

This happened to me twice on different maps (Deep Forest and another one I can't remember). They can be chopped free, I guess, as a workaround.

However, the random map generation code should place the relics after forests are generated and/or account for passability when placing them.

[Freagarach]

Catafalques are placed last, and are placed next to GAIA objects. I indeed don't think we account for passability.

[Salesome]

Related to ​#5858

This is basically the same problem with entity placement inside trees on map generation.

[Stan]

Unlikely to get done for A26

[Freagarach]

Pushing back.