function GatherSplit(const MaskVec: TVec; const NotMaskVec: TVec; const Mask: TVecInt): Vector;
Gather a vector, split to two vectors.
Returns: Vector
Remarks:
If the elements of a vector have been split with a Mask and the "positive" elements have been stored in the MaskVec and "negative" elements have been stored in the NotMaskVec, this routine will restore the original vector.
The length of the MaskVec vector must be equal to the number of ones in the Mask vector. The length of the NotMaskVec vector must be equal to the number of zeroes in the Mask vector.