Incorrect style in HydrostaticFreeSurfaceModel constructor

[glwagner]

I think this changed recently so I wanted to bring up the fact that these constructors incorrectly use TitleCase when they should use camel_case (because they do not construct types):

Oceananigans.jl/src/Models/HydrostaticFreeSurfaceModels/hydrostatic_free_surface_model.jl

Lines 199 to 200 in fe4123f

	Gⁿ = HydrostaticFreeSurfaceTendencyFields(velocities, free_surface, grid, tracernames(tracers)),
	G⁻ = PreviousHydrostaticTendencyFields(Val(timestepper), velocities, free_surface, grid, tracernames(tracers)),

More specifically HydrostaticFreeSurfaceTendencyFields is a legacy constructor whose style should be changed. Unfortunately, for some reason PreviousHydrostaticTendencyFields got added recently with incorrect style so this will need to be changed as well.