Vectorize BigInteger's IBinaryInteger implementation

[alrz]

Most of these methods have a vectorized version in TensorPrimitives which could be used on _bits perhaps with some threshold on the size.

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[huoyaoyuan]

Currently S.R.Numerics is inbox, and thus can't take a dependency on S.N.Tensors.
The optimization of BigInteger is still in the backlog. There are also other potential tasks.

[jeffhandley]

Moving into the Future milestone along with the other BigInteger items.