because that works under wayland out of the box and gtk3 uses it already

Change-Id: Iefaac31e325534a81a5389f752804af917c1baef
Reviewed-on: https://gerrit.libreoffice.org/31213Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>