move IsShowOutlineContentVisibilityButton out of header to avoid having to add extra include paths to all the unit test makefiles. Change-Id: I2763390e07cd85b8f09b6f2ad7702039daecb22f Reviewed-on: https://gerrit.libreoffice.org/c/core/+/105100 Tested-by: Jenkins Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>