These control characters are Writer implementation details and should
not be available via public interfaces.

This filter is also used by SwXTextRange::getString().

Change-Id: If656ee3d451dbefe2f7a905e8b63a44cdb787809
(cherry picked from commit ab4f53ea)
Reviewed-on: https://gerrit.libreoffice.org/35862Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>
(cherry picked from commit 5254a7d1)