Take advantage of MFEM 4.6 Features

[JustinPrivitera]

We should take advantage of new MFEM 4.6 features after #19112 is merged.

FWIW: I would like to offer my assistance in this endeavor. My visit development work is virtually non-existent. But I have a vested interest. I have developed the NURBS FE in MFEM, and have recently implemented a H(div) and H(curl) NURBS elements. The fact that visit can natively access the NURBS FE is a supersuper nice feature!! Particularly, the refinement level machinery.

Issues:

• Visit 3.4.0 does not seem to visualize VectorFE (ND & RT) due to issue with the GetTransferOperator call.
• I would like to add the option to directly access the derivative (gradient, div, curt, laplacian, hessian) of the MFEM basis functions. It seems the GetTransferOperator would need to be generalized for this.

Originally posted by @IdoAkkerman in https://github.com/visit-dav/visit/issues/19078#issuecomment-1833455417

[JustinPrivitera]

@IdoAkkerman Yes, we are happy to have help with this even if it's testing your use cases.

We are working on an update to 4.6.0.

Do you have suggestions for logic changes to support hdiv?

For the direct derivatives, we would need to update the plugin to expose the derivative-based functions as new variables. That will take a bit more time and effort, but to speed things up we could work on a branch together.

Originally posted by @cyrush in https://github.com/visit-dav/visit/issues/19078#issuecomment-1839204609

[JustinPrivitera]

We would also like to update CI docker container to build MFEM.

[cyrush]

the first feature (vector field plotting) is tracked by #18700

[cyrush]

This ticket will track:

I would like to add the option to directly access the derivative (gradient, div, curt, laplacian, hessian) of the MFEM basis functions. It seems the GetTransferOperator would need to be generalized for this.