Add 3D Cartesian Shallow Water Equations

[amrueda]

This PR adds the 3D Shallow Water Equations (SWE) in Cartesian form, which can be solved on a 2D manifold embedded in 3D. We add two strategies to obtain entropy (total energy) conservation based on two-point fluxes: (i) using an entropy correction term, and (ii) using an entropy-consistent projection of the momentum. Both strategies require divergence-free metric terms on the 2D manifold. In this PR, we implement the curl-invariant form of Kopriva (2006). We also add the possibility to discretize the equations with the weak-form kernel.

[codecov]

Codecov Report

Attention: Patch coverage is 92.30769% with 21 lines in your changes missing coverage. Please review.

Project coverage is 84.71%. Comparing base (30bdb23) to head (7a42b0f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/equations/shallow_water_3d.jl	88.31%	18 Missing ⚠️
...vers/dgsem_p4est/dg_2d_manifold_in_3d_cartesian.jl	91.89%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #36      +/-   ##
==========================================
+ Coverage   82.31%   84.71%   +2.39%     
==========================================
  Files           8       11       +3     
  Lines         854     1125     +271     
==========================================
+ Hits          703      953     +250     
- Misses        151      172      +21     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[tristanmontoya]

LGTM!