Blender Git Loki

Fix sculpt neighbor iterator not taking visibility into account

Sculpting tools are designed to ignore hidden geometry and behave like
hidden geometry does not exist.
When getting the neighbors of a vertex, now this takes into account
hidden geometry to avoid returing neighbors which connected edge is not
visible. This should make corner cases of a lot of tools work properly,
especially when working in low poly meshes when is common to have a
single face loop hidden.

Reviewed By: JacquesLucke

Differential Revision: https://developer.blender.org/D11007