The algorithm used for the BVH:
1) first create 1 leaf per primitive (triangle/aabb/instance)
2) Then create internal layers from the bottom up until we are left with
1 node in the top layer. Node i in the layer will have children
(i*4+0) ... (i*4+3) in the previous layer.
This results in a very naive algorithm but it is also very simple to implement.
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11078>
