The broad-phase is used for computing pairs and performing volume queries
and ray casts. It does not persist pairs; it reports potentially new pairs.
It is up to the client to consume the new pairs and to track subsequent
overlap. (b2BroadPhase)
Find new proxy pairs for everything in the move buffer and create their
contacts, in deterministic move-array order. Also rebuilds the dynamic and
kinematic trees and clears the move buffer. (b2UpdateBroadPhasePairs —
serial port of b2FindPairsTask/b2UpdateTreesTask)