This as a side effect also implements support for DOCX <w:pgNumType
w:fmt="decimal" .../>.

Change-Id: I747c3f610dc13f614b6f962c2a498c987765ebb6
Reviewed-on: https://gerrit.libreoffice.org/24457Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>