This enables a relax operation that works only on face sets boundaries, which smooths the jagged edges that are produced when painting or expanding face sets by sliding the topology without affecting the shape of the mesh. This has many uses in hard surface sculpting for things like sculpting panels or smoothing surfaces. It can also help when working with remeshed topology as it makes the face sets looks better and more organized if needed. The operation is implemented as an Shift smooth in the Draw Face sets tool, similar to the Slide/Relax tool. The same operation is also available in the mesh filter to smooth all the face sets boundaries uniformly or to smooth the face set under the cursor with the Use Face Sets option. Reviewed By: brecht Differential Revision: https://developer.blender.org/D7034