Tpetra: missing impl_scalar_t in recent changes in block Crs matrix helpers

[maartenarnst]

@jgfouca @csiefer2

@trilinos/tpetra

Bug Report

We are compiling Trilinos with the complex double type enabled. We are seeing a compilation error when the file Tpetra_BlockCrsMatrix_Helpers_def.hpp is compiled:

INFO:root:#21 1363.9 .../packages/tpetra/core/src/Tpetra_BlockCrsMatrix_Helpers_def.hpp:574:22: error: reference to __host__ function 'operator complex' in __host__ __device__ function
INFO:root:#21 1363.9         const Scalar value = values(row_nnz);

I think I tracked it down to this commit:

• fda2e87#diff-3f68694d20275e6ffbf486fbdf35580b901da77be1a8065115d71ef9e9c236a0

which moves some code into Tpetra_BlockCrsMatrix_Helpers_decl.hpp from shylu but doesn't seem to take into account that there's the implementation scalar type in Tpetra.

I'll introduce a PR with a fix.

[csiefer2]

@maartenarnst That looks reasonable. Thanks for the fix!

[maartenarnst]

Closing this because #12236 was merged.