Better handling of input/output sortedness for spgemm

[brian-kelley]

Right now, spgemm (TPLs) require A and B to be sorted, while our native impl allows unsorted inputs. In many cases (like Tpetra) the user will know whether the matrices are sorted, but we don't give them a way to pass that information to us.
We also promise users that C is always sorted, even though that can add some cost (we have to explicitly sort the outputs from native and MKL).

Not all TPLs necessarily require sorted inputs:

• rocsparse allows unsorted inputs (as long as the max intermediate products per row is <= 8192). An error code is returned if this is exceeded and an input is unsorted: https://github.com/ROCm/rocSPARSE/blob/develop/library/include/rocsparse-types.h#L423
• cusparse reuse requires sorted, but non-reuse does not
• mkl mkl_sparse_sp2m seems to not require sorted inputs