Create a thin film below grounded ice for meshes with ice-shelf cavities

[cbegeman]

Work-in-progress: changes needed to support a thin mesh below grounded ice

Checklist

• User's Guide has been updated
• Developer's Guide has been updated
• API documentation in the Developer's Guide (api.rst) has any new or modified class, method and/or functions listed
• Documentation has been built locally and changes look as expected
• The E3SM-Project submodule has been updated with relevant E3SM changes
• The MALI-Dev submodule has been updated with relevant MALI changes
• Document (in a comment titled Testing in this PR) any testing that was used to verify the changes
• New tests have been added to a test suite

[cbegeman]

Expansion-based smoothing produces bed_elevation > 0.

This commit 124942c will be used to cull these cells until another solution is found.

[cbegeman]

@xylar Here's the branch I've been working from, with your commit added. Remove the last commit to reproduce the smoothing issue (I used expand_factor = 2).

[cbegeman]

Testing

I used the following command:

compass suite -s -c ocean -t icoswisc_mali -w ${WORKDIR} -p ${MODEL_PATH}

with compass/ocean/suites/icoswisc_mali.txt:

 ocean/global_ocean/IcoswISC/MALI_topo_AIS_4to20km/mesh
 ocean/global_ocean/IcoswISC/MALI_topo_AIS_4to20km/WOA23/init
 ocean/global_ocean/IcoswISC/MALI_topo_AIS_4to20km/WOA23/performance_test
 ocean/global_ocean/IcoswISC/MALI_topo_AIS_4to20km/WOA23/dynamic_adjustment

[xylar]

This branch should be rebased onto main, now that #932 is merged, whenever you have a chance.