Warn when interpolation is taking place in vis

[inducer]

(Especially/only) if orders match, because then it might be unexpected.

cc @shawnl00

[alexfikl]

Is the existing warning not sufficient? What other cases should it warn about? https://github.com/inducer/meshmode/blob/b15327fc8a1a6f7494d0562fa0de0d60de05b1da/meshmode/discretization/visualization.py#L1322-L1325

[inducer]

No, not in this case. This code:

pre_density_discr = Discretization(
    actx, mesh, InterpolatoryQuadratureGroupFactory(target_order)
    )

vis = make_visualizer(actx, pre_density_discr, target_order)

makes pre-density as GL and vis as GLL, I think. The warning didn't fire.

[alexfikl]

No, not in this case. This code: makes pre-density as GL and vis as GLL, I think. The warning didn't fire.

Ah, yeah, it wouldn't fire in that case. I'm not sure how I feel about making that a warning though.. all the visualizers in pytential will complain :(

Definitely could use better documentation for when it interpolates and to what elements.