Fix levels having incorrect GlobalTransform the first frame

[johanhelsing]

The transform propagation system runs in the PostUpdate stage, so spawn the levels before PostUpdate so they have time to propagate, but after ProcessApi, so they'll be ready the next frame (assuming the LdtkWorldBundle will be spawned during the Update) stage.

I ran into this bug because in my game I scale the levels, and collision detection is therefore way off during the first frame sending my player character flying.

[Trouv]

I have to give this some thought. I'd prefer not to add another stage if possible, but I can't think of a way to off the top of my head. One reason I wanted to put level spawning before Update was so that users could flesh out entities using the "blueprint pattern" (querying for Added<EntityInstance> or Added<MarkerComponent>) during Update and not have any frame delay. Though, this seems like a reasonable concern too.