This adds a property that checks the normals of each vertex against the
view direction to decide if they should be masked (similar to the
"Front Faces Only" option works for brushes.
{F8739601}
It is only implements for Lasso Mask as Box Mask uses the
View3D_OT_select_box operator. It should probably be refactored into its
own operator int a later patch as it is not really a selection, so it
both can include more sculpt mode related functionality.