BVH improvements

[adayton1]

Summary

• This PR is a feature
• It does the following:
  • Adds a constructor to BVH at the request of myself (see below)
  • Avoids unnecessary copy of each bounding box

Current pattern

axom::spin::BVH<3> bvh;
bvh.setAllocatorID(allocatorID);
bvh.initialize(boxes, numBoxes);

New pattern

axom::spin::BVH<3> bvh(boxes, numBoxes, allocatorID);

[adayton1]

My only concern is that initialize returns a bool indicating whether construction succeeds. But it looks like it always returns true, so it's probably not worth worrying about.

[white238]

"Avoids unnecessary copy of each bounding box"

@adayton1 have you ever thought that maybe we want to do extra work?!?! Why do you have to make everything so efficient and better?

[adayton1]

/style