WIP: Standard weak-form DG for the spherical shallow water equations in covariant form

[tristanmontoya]

This extends upon #31. Now we can solve the shallow water equations in covariant form with P4estMesh, although nearly all of the kernels called by rhs! had to be rewritten. All the geometric terms are computed independently of the particular mesh (does not require structured grids) so it should extend to other grid types like icosahedral, etc. without too much effort.

[codecov]

Codecov Report

Attention: Patch coverage is 91.58700% with 44 lines in your changes missing coverage. Please review.

Project coverage is 85.59%. Comparing base (7079c44) to head (bf01678).

Files with missing lines	Patch %	Lines
...em_p4est/containers_2d_manifold_in_3d_covariant.jl	76.74%	30 Missing ⚠️
src/callbacks_step/save_solution_covariant.jl	80.95%	12 Missing ⚠️
...vers/dgsem_p4est/dg_2d_manifold_in_3d_covariant.jl	98.55%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #37      +/-   ##
==========================================
+ Coverage   81.78%   85.59%   +3.81%     
==========================================
  Files           8       14       +6     
  Lines         829     1340     +511     
==========================================
+ Hits          678     1147     +469     
- Misses        151      193      +42     

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