Change to multiphase hybrid coupling - nodal projection

[mbkuhn]

Summary

Previously, spurious currents in multiphase hybrid cases were reduced by not coupling the nodal projection directly to the incoming pressure values. We have found issues with that, and the proposed change is coupling single-phase regions directly and loosely coupling around the interface. Still needs some more testing.

Pull request type

Please check the type of change introduced:

• 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

Changes to regression tests of exawind-driver will go along with this, but they run fine with a few tweaks.