For version 3 scripts, using script-fu-register-filter
Widgets for SF-OPTION and SF-DIRNAME
Fixes#9992
Test case is Sphere v3.
Note that SF-VECTORS is still not supported,
until there is a VectorsChooser widget in libgimp.
A step towards deprecating old-style scripts using script-fu-register,
and deleting script-fu-interface, the duplicate dialog for SF.
But we still need to change or replace script-fu-register (for non-filter plugins)
to use GimpProcedureDialog.
