Add XML dumping of the new 'SwExtraRedlineTbl'

Change-Id: Ifeba2d07391258ebf55ff3aa9f604e679cc5d7c9
Reviewed-on: https://gerrit.libreoffice.org/7824
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>