init_rigid_bodies should run after TransformPropagate

[LeshaInc]

init_rigid_bodies should run after TransformPropagate, since it uses GlobalTransform when Position is missing.

Otherwise newly spawned entities fall back to (0, 0, 0) position.

This would mean that new entities would start moving according to physics only on the next frame. To mitigate that, transform propagation could be run twice — before and after the physics. The 'before' system can have a condition to run only if there are added rigid bodies.

Fixing this should make child colliders possible (at least for static bodies).