Relax restriction on PC plot point geometry constant coloring

[markcmiller86]

This is requested by E3SM team, @iulian787 and @vijaysm.

On the Pseudocolor plot, Data tab, there is an option to render geometry as surfaces (2D), wireframe (1D) and points (0D). surfaces is the default and when used, it colors the surfaces using the data values and color table often doing an interpolation of some kind.

But, for wireframe and points it ignores data values entirely and colors all entities the same color. Why does it need to do this? I don't think it does. I think it is far more useful to continue coloring the geometry in the same way the surfaces case is handled. Doing so allows one to draw something like a Pseudocolor plot of global node ids but to optionally turn off the interpolation of that data (which honestly makes no practical sense).