Reimplemented method cell_face_as_dense in the grid class

[keileg]

Proposed changes

Changes:

1. Replaced the (8 year old!) implementation of cell_face_as_dense in the Grid class. The new implementation is much more transparent, and documented.
2. Renamed the method cell_face_as_dense -> cell_faces_as_dense.
3. Improved the test for this method.

@IvarStefansson @IngridKJ: Although the test suite is much improved, the old implementation did not fail on this expanded set. I am not sure which grid you used to make the method fail today, but could you test the new version and see if it works? If so, I am not sure if we should expand the test suite with the previously failing grid, so let me know what you think. If it still fails, we will definitely add it.

Types of changes

What types of changes does this PR introduce to PorePy? Put an x in the boxes that apply.

• [ ] Minor change (e.g., dependency bumps, broken links).
• [ ] Bugfix (non-breaking change which fixes an issue).
• [ ] New feature (non-breaking change which adds functionality).
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected).
• [x] Testing (contribution related to testing of existing or new functionality).
• [x] Documentation (contribution related to adding, improving, or fixing documentation).
• [x] Maintenance (e.g., improve logic and performance, remove obsolete code).
• [ ] Other:

Checklist

Put an x in the boxes that apply or explain briefly why the box is not relevant.

• [x] The documentation is up-to-date.
• [x] Static typing is included in the update.
• [x] This PR does not duplicate existing functionality.
• [x] The update is covered by the test suite (including tests added in the PR).
• [ ] If new skipped tests have been introduced in this PR, pytest was run with the --run-skipped flag.

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[IngridKJ]

I performed a quick check with my previously failing grid, and things seem to be working fine now. What I did was simply running my script in the new branch, and I do not get the dimension mismatch I got previously. So, the grid seems to be working fine now. Are you interested in the details or code for the grid which failed, @keileg?

[keileg]

Are you interested in the details or code for the grid which failed, @keileg?

No, I think we are good. Do you agree, @IvarStefansson?

[IvarStefansson]

Are you interested in the details or code for the grid which failed, @keileg?

No, I think we are good. Do you agree, @IvarStefansson?

Yes. Merging. Thanks for fixing, @keileg!