We really don’t want anyone to subclass these classes and introduce new
text layout inconsistencies.

Change-Id: I38d046dc2fab602fd262dc43ac86b55fb0c59db2
Reviewed-on: https://gerrit.libreoffice.org/54153Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Khaled Hosny <khaledhosny@eglug.org>