Fix point picking with render points as spheres

Addresses issue #17223

The issue was that when points were rendered as spheres during point picking. The zbuffer could be initialized with the spheres. Then in the next pass the coincident code is supposed to move the zbuffer values a bit closer to make sure they show up but the zbuffer calc code in render as spheres was overriding the coincident code (all the time actually)

This change makes it so that the coincident code still has an impact even with render points as spheres.

At the same time simplify the coincident code back to it's simpler previous version now that surface with edges no longer relies on it.