On Intel arch, ExtractMostSignificantBits for 512 bit vectors requires the use of the AVX512 opmask (K) registers. This task is to implement the capability of ExtractMostSignificantBits for Vector512 using a single opmask register. This is to allow Vector512 to be used in optimization, but without the implementation overhead of implementing full opmask register support in the register allocator, which will come at a later date.