chore: Add SAS as a common initialism to structfield

[gmlewis]

Relates to: #4035.

cc: @amreshh

[gmlewis]

Note to @amreshh - once you merge master into your PR branch you might need to rm the old custom linter in this repo's bin directory before running your scripts again:

$ ls -l bin
total 234952
-rwxr-xr-x@ 1 glenn  staff  43625954 Feb 25 20:07 custom-gcl
-rwxr-xr-x@ 1 glenn  staff  60976114 Feb 25 20:06 golangci-lint
-rwxr-xr-x@ 1 glenn  staff  15688338 Feb 28 14:58 metadata

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.08%. Comparing base (ca13c0c) to head (e1b79a8).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4054   +/-   ##
=======================================
  Coverage   94.08%   94.08%           
=======================================
  Files         207      207           
  Lines       19220    19220           
=======================================
  Hits        18084    18084           
  Misses        938      938           
  Partials      198      198           

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