Use popcount hardware intrinsics to vectorize TensorPrimitives.PopCount for sizeof(T) == 1 on platforms that have intrinsics.

I tried doing this more generally on other platforms with:

Vector128<byte>lookup=Vector128.Create((byte)0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4);Vector128<byte>cnt1=Vector128.Shuffle(lookup,x.AsByte()&Vector128.Create((byte)0xF));Vector128<byte>cnt2=Vector128.Shuffle(lookup,(x.AsByte()>>4)&Vector128.Create((byte)0xF));return(cnt1+cnt2).As<byte,T>();

and the equivalent for Vector256/512, but it ended up being ~5x slower than just using the scalar byte.PopCount for each element. I also tried using this with SumAbsoluteDifferences in support of sizeof(T) == 8, and it ended up being an order of magnitude worse.