[broadphase] update() should be no-op for the dynamic axis-aligned bounding-box tree when no collision object changes its bounding volume.

[DamrongGuoy]

Currently the update() function of DynamicAABBTreeCollisionManager<> changes the structure of the tree even though no collision objects changes its bounding volume. The updated tree is still valid; however, it can switch the order of the two potential colliding objects (A,B) to (B,A). As a result, the subsequent narrowphase algorithm may give a different answer within a certain tolerance.

The update() function involves removing and inserting the same leaf nodes in HierarchyTree. As a result, it is non-trivial to maintain exactly the same node ordering in the tree. One possible solution is to add a dirty bit in the node to decide whether the tree needs updating.