set_inflow routine for MAC velocity (enforce Dirichlet BC prior to MAC projection)

[mbkuhn]

Summary

For better boundary conditions, there is a need to enforce/populate the MAC velocity at valid boundary cells. Implementing a set_inflow routine, similar to what's used for the nodal projection, is a method to do that.

Pull request type

• [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

The following is included:

• [ ] new unit-test(s)
• [ ] new regression test(s)
• [ ] documentation for new capability

This PR was tested by running:

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

Additional background

Issue Number: