intel/rt: Add support for hit attributes

intel/rt: Add support for hit attributes

For triangle geometry, the hit attributes are always two floats which
contain the barycentric coordinates of the hit.  For procedural
geometry, they're an arbitrary blob of data passed from the intersection
shader to the hit shaders.  In our implementation, we stash that data
right after the HW RayQuery in the ray stack.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7356>