This commit adds the Mask from Boundary operator, which creates or
otherwise modifies a mask based on the the mesh boundary or the face
set boundaries of the mesh.
Conceptually, it behaves similarly to the corresponding automasking
options and the existing Mask from Cavity operator. When applying this
setting, it either uses the global scene value, the brush specific
value, or the operator-defined values. As such, it is exposed in the
existing automasking menus and inside the main Mask menu in Sculpt mode.
Based on this [1] RCS request.
[1] https://blender.community/c/rightclickselect/DYKy/
Pull Request: https://projects.blender.org/blender/blender/pulls/127787
591f4c0e59