BB-54: Operations involving implicit Kronecker product

[mcmillan03]

GraphBLAS rarely needs the kronecker product function but rather an implicit kronecker product. Something like:

kron_mxv(y, A, B, v)

This would create a result vector y as if it did the following sequence:

C=kron(A,B)
y = C*v

But it never generates C. It is possible to use the non-blocking interface for this but I wonder if we would be better off with a direct function. Otherwise, it is fairly unlikely for the implementers to anticipate this use case an capture it.