Blender Git Loki

Fix T40222 texture painting on mirrored meshes does not apply pixel
bleeding at the symmetry edges.

We need an extra way to detect if faces overlap here. An easy way is to
detect the winding of the faces in UV space. If the winding differs, the
faces will naturally overlap. I have tried a few approaches here such as
choosing an offset point from the middle of the edge for intersection in
both faces of the edge in uv space, but winding is the safest way and
should work with very small faces/dense meshes too.