Add RRS6to18 and RRSwISC6to18 meshes

[xylar]

In a later PR, these will be fully vetted and become the E3SMv3 versions of the oRRS18to6v3 mesh.

Checklist

• User's Guide has been updated
• Developer's Guide has been updated
• API documentation in the Developer's Guide (api.rst) has any new or modified class, method and/or functions listed
• Documentation has been built locally and changes look as expected
• Document (in a comment titled Testing in this PR) any testing that was used to verify the changes
• New tests have been added to a test suite

[xylar]

Based on #575, so needs to be rebased after than PR gets merged.

[xylar]

Progress:

• base mesh - takes 28 hours (on a login node)
• remap topography - takes 4096 cores
• culled mesh - requires using the step directory as the temp directory for cull() calls
• initial condition - hangs on loading tracer lat/lon from woa23.nc
• performance test
• dynamic adjustment
• files for E3SM

[xylar]

Testing

The full set of test cases is being run on Chrysalis at:

/lcrc/group/e3sm/ac.xylar/compass_1.2/chrysalis/test_20230809/rrswisc6to18

Progress so far:

• base mesh
• remap topography
• culled mesh
• initial condition
• performance test
• data ice-shelf fluxes
• dynamic adjustment
• files for E3SM -- seaice_graph_partition isn't done but proceeding as expected; ocean_graph_partition can't make partitions bigger than 746496 tasks because of a gpmetis error but this is a ludicrously large count.