optional gmsh integration for rectangles and boxes.

[cfrontin]

Purpose

Adds optional gmsh-based recreation of default box and rectangle grids.

• adds new enum case for yaml input mesh_type: gmsh; when specified gmsh grids are used
• grid stretching is toggled by hardcoded param, probably should be made an input
  • runs gmsh on stretched box to get an isotropic unstructured grid
  • relaxes stretching of box to get unstructured grid with specified aspect ratios
• my VS code automatically killed some trailing whitespace also, so that's in the commit too. fwiw adding ?w=1 to comparison URLs on GH ignores whitespace-only changes in the diff

Type of change

What types of change is it?
Select the appropriate type(s) that describe this PR

• New feature (non-breaking change which adds functionality)

Testing

• add new test case(s) to tests/9_Regression?

Checklist

Put an x in the boxes that apply.

• I have run existing tests which pass locally with my changes
• I have added new tests or examples that prove my fix is effective or that my feature works
• I have verified my code additions work in parallel
• I have added necessary documentation
• I have made sure the GPL virality concerns are not an issue for incorporation into NREL WindSE

[cfrontin]

sorry if i stepped on your toes! i didnt mean to push my fix-it commit.

[jefalon]

lol, No worries, I wasn't working particularly fast. I was having problems getting the demos to run correctly. I think it's fixed. Hopefully it passes CI (though it seems stuck on the parallel case)

[cfrontin]

Hmm, from my memory related investigations, I think that the mesh will be meshed (hopefully identically) on every single processor. I think some kind of "rank == 0" operation should happen on this line and the others like it... I think also we'd have to get the variable called dir_to_meshes to be shared across the other ranks so that dummy.xml can be accessed by all processes once it's done? the thing is i know nothing about is how to deal with this in a fenics-friendly way @eyoung55 and @jefalon