fdo#84938: replace EVENT_ constants with enum

Change-Id: I8275832d8dae43b374bddd48520d11592e9a6a1f
Reviewed-on: https://gerrit.libreoffice.org/13134
Tested-by: LibreOffice gerrit bot <gerrit@libreoffice.org>
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>