FEM-based Linear Sweep

[rchen20]

Summary

• This PR is a feature
• It does the following:
  • Adds a FEM-based linear sweep algorithm at the request of the DT team.
• Some caveats:
  • There is only one problem size available due to the need for a mesh generator. As a result, the mesh parameters are contained in FEMSWEEP_DATA.hpp. The transport team will work on duplicating mesh generation logic in the near future.
  • Some problem parameters are a function of the mesh generation, which results in magic numbers at the moment.

[rchen20]

Hello @LLNL/raja-core, this PR is ready to go. Please review when you can!

[artv3]

Awesome work @rchen20 !

[artv3]

Any chance we can add the SYCL variant? We have a few examples in other FEM kernels that should help guide the implementation here.

Not part of the goals....