mostly so that the subclasses can use proper enum types for their own
IDs.
It turns out that nothing at the svl/sfx2 level needs an ID anyhow.

Change-Id: I3c020aeafb812fa30d896216d4e3bc1a82cbfeab
Reviewed-on: https://gerrit.libreoffice.org/35222Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>