Standardize code in calc_sfc_displacement

[Hallberg-NOAA]

Slightly modified the recently added subroutine calc_sfc_displacement to
document the units of its variables and to follow the MOM6 code standards from
https://github.com/NOAA-GFDL/MOM6/wiki/Code-style-guide. The changes include
white-space corrections, changing logical comparison syntax like '.gt.' to '>',
and explicitly identifying where array syntax is used. All answers and output
are bitwise identical.

[codecov]

Codecov Report

Merging #58 (0e54bdd) into dev/gfdl (d838ccd) will not change coverage.
The diff coverage is 0.00%.

@@            Coverage Diff            @@
##           dev/gfdl      #58   +/-   ##
=========================================
  Coverage     28.95%   28.95%           
=========================================
  Files           242      242           
  Lines         71556    71556           
=========================================
  Hits          20716    20716           
  Misses        50840    50840           

Impacted Files	Coverage Δ
src/initialization/MOM_state_initialization.F90	19.83% <0.00%> (ø)

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[MJHarrison-GFDL]

I approve.

[Hallberg-NOAA]

Matt Harrison has reviewed and approved this PR, which is essentially an appendix to PR #41.

This PR has passed TC testing and pipeline testing at https://gitlab.gfdl.noaa.gov/ogrp/MOM6/-/pipelines/14535.

I would appreciate it if someone else with the right authorities could please click on the "Approve" button, and then the green button to merge in this PR.

[marshallward]

Approved on behalf of @MJHarrison-GFDL (for real this time).

[marshallward]

Gaea regression: https://gitlab.gfdl.noaa.gov/ogrp/MOM6/-/pipelines/14553 ✔️