BVH query tolerance should be relative to either the AABB bounds or the total "scene" bounds

[gzagaris]

Currently, the BVH has a default tolerance or the caller can set a tolerance in an ad hoc way.

@mclarsen suggests that a better approach may be to set the tolerance relative to the AABB or perhaps the total "scene" bounds, i.e., bounds of the root BVH bin (?)

[kennyweiss]

This is a good idea. We should address this when needed.