Add an option for doing p-refinement on elements marked for refinement

[YaqiWang]

Reason

Currently, we use markers to mark elements for refinement. When we do refinement, we always do h-refinement, i.e. cut the elements. It will be nice to have an option to do p-refinement instead of doing h-refinement. It is appealing for discontinuous FEM because it does not make the mesh non-conforming (i.e. having hanging nodes or mismatched faces).

Design

@roystgnr mentioned there is a function call mesh_refinement.switch_h_to_p_refinement() that we can use for this, which looks something we can quickly implement.

Impact

A capability that allows users to enhance their DFEM solution without changing the mesh.

[lindsayad]

@roystgnr is there much more to do here than call switch_h_to_p_refinement()? I guess naively I feel like our marker system overall should work irrespective/agnostically of h or p refinement, but maybe I'm wrong

[roystgnr]

For pure p refinement that's actually all you need. The optimal choices of fractions to mark can differ in the case of adaptive refinement, but no much as you'd care. And for a priori refinement like Yaqi wants that's irrelevant.

Things don't get iffy until you look at hp refinement; figuring out where to choose h over p is a much more involved question unless you know where every singularity is a priori.

[zachmprince]

Another comment related to this issue. To support third order shape functions in 3D we might have to address this error:

*** ERROR ***

Max quadrature points per element assumptions made in some code (e.g.  Coupleable and MaterialPropertyInterface classes) have been violated.
Complain to Moose developers to have constMaxQpsPerElem increased from 216 to 343

[lindsayad]

Ok @roystgnr per our discussion last Thursday, I'm going to assign myself to this one