Add 2D Compressible Euler with Gravity

[MarcoArtiano]

This PR adds the 2D compressible Euler Equations with gravity where the prognostic variables are density, momentum and kinetic plus internal energy, instead of the total energy as in #79.

I have few questions about the name, at the moment I decided for CompressibleEulerInternalKineticEnergyEquationsWithGravity2D, however I'm not sure whether this is the best option, to differentiate it by CompressibleEulerEquationsWithGravity2D where the total energy is the prognostic variable.

Other suggestions may be:
CompressibleEulerInternalAndKineticEnergyEquationsWithGravity2D
CompressibleEulerKineticInternalEnergyEquationsWithGravity2D
CompressibleEulerKineticAndInternalEquationsWithGravity2D

Do you have any suggestions @benegee, @tristanmontoya, @amrueda?

Hendrik suggested CompressibleEulerEnergyEquationsWithGravity2D.

• Add type tests
• Add inertia gravity wave and test

To do in new PRs:

• Add baroclinic instability
• Add mountain Schaer
• Add linear hydrostatic
• Add linear nonhydrostatic

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.10%. Comparing base (9d6bbf5) to head (80cebe5).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #119      +/-   ##
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+ Coverage   96.88%   97.10%   +0.21%     
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  Files          28       29       +1     
  Lines        3369     3621     +252     
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+ Hits         3264     3516     +252     
  Misses        105      105              

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[ranocha]

Thanks! Just a minor round of comments.

[MarcoArtiano]

@ranocha I've changed the name accordingly and added the comment. This is ready for the final round of review. Thanks!

[ranocha]

Thanks!