[FEATURE] Distance queries for the primitives (distance to surface)

[cstatz]

Is your feature request related to a problem? Please describe.
Provide an interface to query the (closest-) distance to the surface from any point in space in or surrounding the scene, preferable using the already existing acceleration structures. This kind of query is useful in many applications involving inhomogeneous materials.

Describe a possible solution.
Implement a distance to surface function for each primitive. Implement a distance traversal for the bvh (check if point is inside bounding box of node).

Describe alternatives you've considered
Using a library that provides the acceleration structured and queries for the primitives.

Additional context
The query would be available in the scene api and provide the prim_id, geom_id, closest_point and closest_distance.

[orgarten]

Currently the following things are implemented in features/distance_to_surface:

• plane

• sphere

• initial implementation for triangles

Still missing:

• cylinder (somewhat complicated, because elliptical shapes are allowed)
• BVH traversal for distance queries (e.g. find primitive to which point P is the closest)

I will keep working on the problem. First, I will complete the triangle implementation and test it properly. Then I will work on the cylinder and the BVH traversal. Might take a week or two.

[orgarten]

BVH traversal is still missing and tests for triangle distance to surface is still missing, everything else is addressed in PR #59.