Add infill density benchmark

[danieldouglas92]

Pull Request Checklist. Please read and check each box with an X. Delete any part not applicable. Ask on the forum if you need help with any step.

Describe what you did in this PR and why you did it.

Before your first pull request:

• I have read the guidelines in our CONTRIBUTING.md document.

For all pull requests:

• I have followed the instructions for indenting my code.

For new features/models or changes of existing features:

• I have tested my new feature locally to ensure it is correct.
• I have created a testcase for the new feature/benchmark in the tests/ directory.
• I have added a changelog entry in the doc/modules/changes directory that will inform other users of my change.

[jdannberg]

These are the comments I made last night (so they are for an older version). I am submitting that review for now and then I'll have a look at the new version.

[jdannberg]

This is great, thank you for contributing this! If you have time, it would also be great if you could add a short description in the manual, but if not, that's fine as well. I mostly have a few suggestions for documentation, but otherwise this looks great!

[naliboff]

@danieldouglas92 - Nice work, this is a really nice contribution! I only have minor questions and comments, and overall the PR is in great shape.

[jdannberg]

I think there were some comments from my first review you did not address (maybe because they were listed as outdated), I copied them here again. Otherwise this looks good!

I haven't looked at the manual text yet (since it does not build yet) and I can do this next after you rebase.

The only other point I remembered: We usually have a test case for each benchmark. You don't need to copy the .prm file, but you can instead include your benchmark prm file in a test and then set the end time to zero (you can see an example of that in sol_kz_2_project_q1_only_visc.prm). The point is to make sure that even if we make future changes in ASPECT, the tester will still execute the files you added and we will notice if it breaks.

[gassmoeller]

/rebuild

[jdannberg]

Great, looks good! Thank you for contributing this!
This is ready to merge once the tester is finished.

[jdannberg]

@naliboff You still have to approve before we can merge this.

[naliboff]

@danieldouglas92 - Nice work, ready to merge!