HydrostaticFreeSurfaceModel dynamics tests on ConformalCubedSphereGrid with fully explicit treatment of the free surface

[navidcy]

To verify that the momentum equation is correctly implemented, we need a few validation tests. These can use ExplicitFreeSurface; getting SplitExplicitFreeSurface to work will be tackled separately. We should set the gravitational acceleration so that the barotropic wave speed is roughly 10x faster than the dynamics velocity (eg low Mach number). We propose 3 tests:

1. Solid body rotation test. This can be implemented by attempting a free running simulation using the velocity field from the tracer advection test.
2. Rossby-Haurwitz test, following https://github.com/CliMA/Oceananigans.jl/blob/main/validation/solid_body_rotation/rossby_haurwitz.jl
3. Freely-decaying barotropic turbulence on the sphere (eg following https://github.com/CliMA/Oceananigans.jl/blob/v0.70.0/validation/near_global_lat_lon/freely_decaying_barotropic_turbulence.jl).

[glwagner]

What's the status of this issue?