Previously .uno:AcceptTrackedChange / .uno:RejectTrackedChange always
worked by cursor position, but redlines are stored in the redline table,
so they have a unique index. Allow specifying that index when invoking
the command, and in that case ignore the cursor position.

The index is not stable after an insertion / deletion.

Change-Id: I493a22e84800ded224fb6b9c61261744dc0fb64f
Reviewed-on: https://gerrit.libreoffice.org/28192Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>