Add conservative remapping of observational datasets onto Greenland Ice Sheet mesh

[trhille]

This merge adds conservative remapping of observational data sets (thickness, bed topography, velocity, and uncertainties) onto the Greenland Ice Sheet mesh, and handles some of the peculiarities of the other gridded datasets (unit conversions, sign conventions, etc).

Checklist

• [x] User's Guide has been updated
• [x] Developer's Guide has been updated
• [x] Documentation has been built locally and changes look as expected
• [x] Document (in a comment titled Testing in this PR) any testing that was used to verify the changes

[trhille]

@andrewdnolan, as of https://github.com/MPAS-Dev/compass/pull/803/commits/62155ab072c4b79b693bcbf9e4db040bdd6b5f35, this runs successfully on one compute node on Perlmutter in ~11.5 minutes. We ultimately want this to follow generally the same workflow as the antarctica/mesh_gen case, so all (or almost all?) of the code that I've added to compass/landice/tests/greenland/mesh.py should be moved to compass/landice/mesh.py.

[andrewdnolan]

Testing

• Machine: perlmutter
• Compass version: 1.3.0-alpha.2

Command run:

compass setup -n 45 -w wrkdir -f custom.cfg

where custom.cfg

[mesh]

levels = 20

min_spac = 6.e3
max_spac = 60.e3

[parallel]
account = m4288

[job]

qos=debug
wall_time = 0:30:00

Results:

landice/greenland/mesh_gen
  * step: mesh
  test execution:      SUCCESS
  test runtime:        10:23
Test Runtimes:
10:23 PASS landice_greenland_mesh_gen
Total runtime 10:27
PASS: All passed successfully!