Another way to fix the UDF MAC fills

[marchdf]

Summary

The dirichlet fill now depends on if we are filling a face-centered or node centered field.

Pull request type

Please check the type of change introduced:

• [x] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] Documentation content changes
• [ ] Other (please describe):

Checklist

This PR was tested by running:

• the unit tests
  • [ ] on GPU
  • [ ] on CPU
• the regression tests
  • [ ] on GPU
  • [ ] on CPU

Issue Number: #1076

[marchdf]

Still need to do it for lev != 0

[marchdf]

This PR has made a lot of people very angry and been widely regarded as a bad move.

(the real reason for closing: templating wont work because for lev != 0 we need to pass in an Array of bc functs and so they need to have the same type. It was fun while it lasted. #1093 should be a better fix)