Use scipy distance_transform_edt to replace slow loop

[trhille]

Use scipy distance_transform_edt to replace slow loop, speeding up get_dist_to_edge_and_gl by orders of magnitude.

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
• The E3SM-Project submodule has been updated with relevant E3SM changes
• The MALI-Dev submodule has been updated with relevant MALI changes
• 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

[trhille]

Testing

Testing on 8–30km Antarctica mesh.
With these changes: compass.landice.mesh.get_dist_to_edge_and_gl() took 0.05 seconds
With previous: compass.landice.mesh.get_dist_to_edge_and_gl() took 57.52 seconds