Implement rigid body helper

[janhohenheim]

Objective

• It's hard to do something for an entire collider hierarchy. e.g. there's no neat way to do a shape cast for an entire rigid body, or find the total AABB for a rigid body

Solution

• Create a helper SystemParam for
  • generating a compound collider of all colliders, translated and scaled as if it was directly on the rigid body
  • generate a world space AABB for all colliders

Testing

• added unit test
• added example

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Showcase

Not needed, as this is rather niche