Filter collisions between children of the same rigidbody in broad phase

[mbrea-c]

Objective

Currently, collisions between multiple child colliders of the same rigidbody are ignored by the solver. However:

• Collision events are generated for such cases.
• All such collisions are processed in the narrow phase, which has a large performance impact in projects that rely heavily on child colliders.

Preferably all such collisions should be filtered out earlier, in the broad phase, to avoid both of these issues.

Solution

• Keep the ColliderParent of a collider in AabbIntervals in the broad phase.
• Ignore a collision if the ColliderParent of two entities is equal.

Changelog

• Collisions between children of the same rigidbody are no longer reported in contact events and are no longer processed in the narrow phase.

[Jondolf]

LGTM, thanks!