Mean value in Zhang-Shu limiter on curved meshes

[andrewwinters5000]

This is a bug fix where all mesh types other than TreeMesh should compute the solution mean value u_mean including the element Jacobians. If this is not done, it is possible to lose conservation. Typically, the values from extra_analysis_errors = (:conservation_error,) in the AnalysisCallback should stay between 1e-13 to 1e-15. However, when one computes the incorrect value for u_mean on a curved mesh these conservation errors might increase to something between 1e-4 to 1e-8 (depending on the setup, how often the limiter is called, and how "warped" the mesh elements are).

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 88.23529% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 96.15%. Comparing base (6e5ff49) to head (9a1d999).

Files	Patch %	Lines
src/solvers/dgsem_structured/dg.jl	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1945      +/-   ##
==========================================
- Coverage   96.15%   96.15%   -0.00%     
==========================================
  Files         454      454              
  Lines       36496    36509      +13     
==========================================
+ Hits        35092    35103      +11     
- Misses       1404     1406       +2     

Flag	Coverage Δ
unittests	96.15% <88.24%> (-<0.01%)	⬇️

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[bennibolm]

LGTM. Thanks