Ice sheet thickness boundary condition

[alex-huth]

Allow assignment of ice shelf thickness (Dirichlet condition) wherever hmask == 3. This seems to have been only partially implemented previously. This commit has been tested by ensuring that modeled ice-shelf evolution can match the analytical "flow-band" ice-flow solution with thickness enforced at the western boundary.

[codecov]

Codecov Report

Merging #474 (5567703) into dev/gfdl (e5b64f9) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

❗ Current head 5567703 differs from pull request most recent head 8d24a1f. Consider uploading reports for the commit 8d24a1f to get more accurate results

@@             Coverage Diff              @@
##           dev/gfdl     #474      +/-   ##
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- Coverage     37.54%   37.54%   -0.01%     
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  Files           270      270              
  Lines         79030    79030              
  Branches      14633    14635       +2     
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- Hits          29671    29670       -1     
- Misses        43892    43894       +2     
+ Partials       5467     5466       -1     

Files	Coverage Δ
src/ice_shelf/MOM_ice_shelf_state.F90	0.00% <ø> (ø)
src/ice_shelf/MOM_ice_shelf.F90	0.00% <0.00%> (ø)
src/ice_shelf/MOM_ice_shelf_dynamics.F90	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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[Hallberg-NOAA]

These changes look good to me, although at some point we might want to reconsider whether ISS%hmask is an array of reals or integers, since it is being used almost every where as though it is an integer. Also, there are some instances of using .ne. in comparisons, whereas the preferred syntax is the more succinct \=. None of these issues is material enough to impact the value of this commit, however, and they might be addressed later.