MapLoader needs love

[metalgearsloth]

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There's pretty much 2 code paths to entity creation in RT: one via maploader deserializing it and another via spawning it ingame which are completely detached from each other where one can break when the other is fine.

I think ideally maploader would build a hierarchy of entities and then spawn them in order rather than initializing everything at once then starting everything at once etc so hopefully we can avoid all of the specific maploader hacks that exist right now.