Broad phase pair filters cannot access body information

The current API for the broad phase pair filter cannot access any information about the bodies that are colliding. The filter has access to the handles via the `BroadPhasePairFilter` trait but there is not way to retrieve the body information from the set due to the fact that `MechanicalWorld::step`, which calls the filter, requires mutable access to the body set. Utilizing the user data on the collider is sufficient for cases where the information does not change during each step (e.g., parent information) but cannot be used for information about a body that may have been updated.