Add the following types of random number generators across all backends to make them consistent

• Mersenne twister (present in cuRand and std::random, not present in clrng)
• xorwow (present in curand, needs cpu and opencl implementations)
• MRG32K3a (present in curand and clrng, needs cpu implementation)
• Threefry (from Random123) (needs to be ported from Random123 to CUDA and CPU backends)
• Philox (from Random123) (needs to be ported from Random123 to all backends)