This implements a new mode in the Face Sets Create operator to create a
new face sets from the faces selection in edit mode. This can be used
when the user considers that the edit mode tools are more convenient for
a more precise control or a certain type of selection, like creating a
face set from a face loop.
Reviewed By: jbakker
Differential Revision: https://developer.blender.org/D7211
48ea173a7d