Implement distance adaptive shadows on the CPU

[Dawoodoz]

This can currently be done by using multiple light sources, but this is quite expensive. A combination of multiple light sources and temporal smoothing of shaking lights can improve the performance. If temporal filtering is applied as motion blur using a cyclic buffer on the final result (diffuse x light), it will look natural even if something moves. If the number of light positions in the loop equals the number of image in the cyclic buffer, the perceived image will be stable by subtracting the oldest image before adding the new image from the same relative translation offset.

If large blocks of illumination are known to have no shadows by not casting from the floor, sampling the depth based shadow maps can then be skipped and save around 80% of the computation time. Regions entirely in shadows can even be skipped completely.

The goal is to look better than Nvidia RTX enabled games (ugly noise filter) and run faster on a budget CPU.