plug-ins: port file-heif to GimpProcedureConfig

and also use an aux argument, seems to work fine.
4 jobs for master in 12 minutes and 56 seconds (queued for 1 second)
Status Job ID Name Coverage
  Babl
passed #444141
babl-git

00:02:54

 
  Gegl
passed #444142
gegl-git

00:02:32

 
  Gimp
passed #444143
build-git-autotools

00:07:30

passed #444144
build-git-meson

00:04:23