This ports the LUT using compute shader.
All LUT are computed by the same compute shader
to avoid boiler plate code to add new LUTs.
As for the generation code itself it is mostly the
same except for the use of `hammersley_2d` instead of
regular grid sampling. Regular grid did not improve
anything and was a bit more cumbersome.
This also bumps the number of samples very high
for more precision.
The new utility class for computing the LUT has
methods to write the content to a PFM image file
or as C++ array header.
7b54fce723