Ocean Waves: target velocity given to added liquid in numerical beach

[mbkuhn]

Summary

Same idea as #1264, but for the numerical beach instead of the wave generation zone

Pull request type

• 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

Likely no diffs on ow_* regression tests because they don't run long enough to hit numerical beach. I'll add a test to change that.

[mbkuhn]

there are very small diffs with ow_linear and ow_stokes, as expected. new regression test is set up to better test numerical beach functionality by initializing with a full wave field, which is present in the outlet region from the very beginning.