Distributed regridding - concrete example

[juliasloan25]

Part of ClimaCoupler SDI #188.

The goal of this PR is to implement a concrete example of distributed regridding. This will allow us to implement the logic for a specific case while interactively viewing and verifying weights, indices, output values, etc. It will also help us better understand the relevant MPI functions and how/when they need to be used.

8/22/23 Update

This PR contains a working prototype of the distributed regridding (in ClimaCoreTempestRemap/test/mpi_tests/distr_regrid_ex_clean.jl). This has been tested on 2 processes when remapping from 2 to 3 elements, and appears correct when compare to serial regridding results.

Future work could include:

• Add quantitative test comparing to the serial result

• Test using more than 2 processes

• Test remapping between different spaces (generalize from 2 -> 3 elements case)

• [x] Code follows the style guidelines OR N/A.

• [x] Unit tests are included OR N/A.

• [x] Code is exercised in an integration test OR N/A.

• [x] Documentation has been added/updated OR N/A.