Refactor dimension-(in)dependent implementation of subcell limiting

[bennibolm]

3D implementation of subcell limiting is coming in #2572 .

Some code in subcell_limiters_2d.jl was actually dimension independent. On the other hand, there was code that was specifically for 2D but was not marked or dispatch that way.

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.76%. Comparing base (79274d9) to head (cabb641).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2573      +/-   ##
==========================================
- Coverage   96.76%   96.76%   -0.00%     
==========================================
  Files         522      522              
  Lines       42473    42472       -1     
==========================================
- Hits        41099    41098       -1     
  Misses       1374     1374              

Flag	Coverage Δ
unittests	96.76% <100.00%> (-<0.01%)	⬇️

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[DanielDoehring]

I have just a few cosmetic comments

[bennibolm]

Thanks! @DanielDoehring