Hardcode CEG particle type aliases

You can give particle types custom names, but literally nobody is doing that:
https://github.com/search?q=explosion_alias+NOT+is%3Afork&type=code

This is because the names decently reflect what the types do, and making yourself incompatible with other games would just be shooting yourself in the foot.

The request is to put the existing basecontent mapping in the engine and remove this ability.