This adds a new way of computing occlusion using visibility bitmask. To
make it more algorithm agnostic, we name it horizon scan.
This cleans-up / simplify the code compared to the Horizon based solution.
There is no more trickery for fading influence of distant samples which
makes the result match cycles closer.
This introduces a new thickness option. Maintaining it relatively low
makes it possible to avoid over occlusion because of in front geometry.
Making it too low will cause under occlusion.
Related #112979
Pull Request: https://projects.blender.org/blender/blender/pulls/114150
0684b68eb4