During slideshow, the combination outline text mode, and highlight background color never worked. Adding cppcanvas code to handle it. Change-Id: I9abb45fca4c89d206ebb431ff5675288e5deab43 Reviewed-on: https://gerrit.libreoffice.org/c/core/+/174872 Tested-by: Jenkins Reviewed-by: Thorsten Behrens <thorsten.behrens@allotropia.de>