Add tokens for 'table cell' redlines (future patch)

This patch adds 2 tokens for future patche's use of table cell
redline preservation.

Change-Id: Ic0ec4122eeaf66c6f0ebff9251fbc38596877541
Reviewed-on: https://gerrit.libreoffice.org/7869
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>