Export redline 'formatting changes' back to DOCX

This patch adds support for the export of any redline 'formatting changes'
properties that were imported from a DOCX file under the
'rPrChange'->'rPr' XML node.

Change-Id: Iffb4ce9f6606013a1f6f937d2e62ef0cf9e015b5
Reviewed-on: https://gerrit.libreoffice.org/6909
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>