Those new functions invert the winding of polygons, effectively inverting their normals.
A helper was also added to allow swapping two items in customdata layers.
Being able to invert normals outside of BMesh area is very important in several places,
like IO scripts or customnormals modifiers...
Reviewers: campbellbarton
Differential Revision: https://developer.blender.org/D1814
877f441628