fdo#73596 Added support to import and export \r,\h Index flags.

This supports \r flag run-in type index. If \r is specified then we don't
have to write \e flag (separator char).
\h is Alphabetic separator, where indexes are grouped as per starting
character.

Change-Id: I690b29cef3d24b2a71b01f1deef0e418162d71aa
Reviewed-on: https://gerrit.libreoffice.org/8099
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>