Add entropy2cons for CompressibleEulerQuasi1D

[jlchan]

This enables modal flux differencing DGMulti solvers, and adds a new test.

This should also retain coverage which decreases after moving SWE to TrixiSWE.jl in #2379.

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.95%. Comparing base (0ae1541) to head (6babc55).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2385      +/-   ##
==========================================
+ Coverage   96.94%   96.95%   +0.01%     
==========================================
  Files         504      504              
  Lines       41717    41721       +4     
==========================================
+ Hits        40440    40448       +8     
+ Misses       1277     1273       -4     

Flag	Coverage Δ
unittests	96.95% <100.00%> (+0.01%)	⬆️

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[patrickersing]

Thanks for adding this!
This looks almost ready to merge, I would just add an additional unit test for the conversion between conservative and entropy variables.

[patrickersing]

LGTM!