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Based on the paper "Practical Hash-based Owen Scrambling" by Brent Burley, 2020, Journal of Computer Graphics Techniques. It is distinct from the existing Sobol sampler in two important ways: * It is Owen scrambled, which gives it a much better convergence rate in many situations. * It uses padding for higher dimensions, rather than using higher Sobol dimensions directly. In practice this is advantagous because high-dimensional Sobol sequences have holes in their sampling patterns that don't resolve until an unreasonable number of samples are taken. (See Burley's paper for details.) The pattern reduces noise in some benchmark scenes, however it is also slower, particularly on the CPU. So for now Progressive Multi-Jittered sampling remains the default. Differential Revision: https://developer.blender.org/D15679