Move subcell limiter func

[DanielDoehring]

See #2588 (comment), #2587 (comment) and #2587 (comment)

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.80%. Comparing base (61ae744) to head (5b97d49).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2591   +/-   ##
=======================================
  Coverage   96.80%   96.80%           
=======================================
  Files         527      527           
  Lines       42609    42609           
=======================================
  Hits        41247    41247           
  Misses       1362     1362           

Flag	Coverage Δ
unittests	96.80% <100.00%> (ø)

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[bennibolm]

@DanielDoehring Now, I'm happy. Maybe you can have one last look and we can merge it then.