Hydrostatic initialization in ice cavities

[MJHarrison-GFDL]

Hydrostatic initialization in ice cavities

 - Iteratively solve for the initial ice shelf displacement in cavities by calculating the pressure at the current displacement depth using the unperturbed profile.
 - This change should obsolete TRIM_IC_FOR_PSURF and DEPRESS_INITIAL_SURFACE for 
    ice shelf applications and should work for arbitrary equations of state. 
 - Existing implementations (e.g. ISOMIP) should turn off the above options in order to exercise
   this feature.
 - This code change should not impact non ice-shelf configurations or those with either of the above two options.
 - Incorporates PR#35 which was needed for testing
 - tested with [this example](https://github.com/MJHarrison-GFDL/MOM6-IceShelf-examples/tree/a6c5348 )
 - no initial truncations in layer and ALE/rho with this feature although ALE/zstar continues to exhibit initial truncations.
 - initial truncations in ALE/zstar deserve further investigation since results should be nearly identical across configurations
   using a linear profile and equation of state.

[codecov]

Codecov Report

Merging #41 (ec27833) into dev/gfdl (2d32631) will decrease coverage by 0.02%.
The diff coverage is 6.45%.

❗ Current head ec27833 differs from pull request most recent head 99989da. Consider uploading reports for the commit 99989da to get more accurate results

@@             Coverage Diff              @@
##           dev/gfdl      #41      +/-   ##
============================================
- Coverage     28.85%   28.82%   -0.03%     
============================================
  Files           242      242              
  Lines         71422    71495      +73     
============================================
+ Hits          20609    20612       +3     
- Misses        50813    50883      +70     

Impacted Files	Coverage Δ
src/ice_shelf/MOM_ice_shelf.F90	0.00% <0.00%> (ø)
src/initialization/MOM_state_initialization.F90	19.83% <5.26%> (-0.90%)	⬇️
src/core/MOM.F90	58.44% <16.66%> (-0.18%)	⬇️

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[Hallberg-NOAA]

This PR is built on top of the changes in MOM6 PR #35, so it should be dealt with after the issues noted with that predecessor PR have been addressed.

[marshallward]

@MJHarrison-GFDL Can you resolve the conflicts when you get a chance?

[marshallward]

@Hallberg-NOAA did you want to review this? Or would someone else be better?

[Hallberg-NOAA]

Overall I like the direction where this PR is going, but I have a number of minor changes that I would like to see made (as spelled out in a series of individual comments) before I think that this PR should be merged into dev/gfdl.

[Hallberg-NOAA]

This PR has passed the TC testing and the pipeline testing at https://gitlab.gfdl.noaa.gov/ogrp/MOM6/-/pipelines/14508. Unfortunately, it changes the order of some entries in numerous MOM_parameter_doc.all files, so these will have to be updated in MOM6-examples as well.