plug-ins: port file-xbm-save to GimpProcedureConfig

and add boolean arguments to control comment and hot-spot
writing. This revives comment writing, which is disabled by default
and comes with a big warning in the dialog.
5 jobs for master in 27 minutes and 9 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Dependencies
passed #459216
deps-git

00:04:38

passed #459217
deps-x86_64-w64-mingw32

00:17:43

 
  Gimp
passed #459218
gimp-autotools

00:09:25

passed #459219
gimp-meson

00:06:12

passed #459220
gimp-x86_64-w64-mingw32-meson

00:09:25