Extend Propper++ to info_overlay projections

[piqey]

The current Propper++ behavior when info_overlay entities are selected is to use the editor helper for the output model and materials:

As there are a number of limitations placed upon the LightmappedGeneric and VertexLitGeneric shaders when used with infodecal and info_overlay (such as incompatibility with bump maps and phong), it would be nice to have Propper++ extended to instead view info_overlays as their projected/overlayed geometry when selected for propping_(?)_, visible in Hammer as the green mesh pictured below:

As of now, I'll be using Blender, shrinkwrap and remesh for something similar, but it's unlikely that solution will result in geometry as optimized as that produced by info_overlay.