Jamie Bramwell

I think this needs an `updateMesh` method in Axom's `MFEMSidreDataCollection` class.

It's entirely possible this was always a bug. It came up in @samuelpmishLLNL 's PR for refactoring ODEs. Looking at the underlying MFEM call, it definitely expects the full dofs...

This may be due to the CG linear solver by default using iterative mode. This means initial guesses for the linear solver must be initialized.

We also need to update the input file-driven tests to call the accelerator initialization routine.

This is already partially documented [here](https://serac.readthedocs.io/en/latest/sphinx/quickstart.html#building-serac).

@barreracruz FYI

Wait, I just realized an error in my calculation. Fix incoming tomorrow.

Thanks for the fix @samuelpmishLLNL ! Adding some tests now...

@btalamini @samuelpmishLLNL @sethwatts @barreracruz Any other thoughts? Now that I have more reasonable examples and documentation, I was going to give another stab at explaining this PR during the meeting...

I found the last subtle bug (thanks @samuelpmishLLNL !) so this branch should now be ready for a final review.