instead of std::unique_ptr, where we end up needlessly putting small
objects separately on the heap

Change-Id: I107421e7530c9580869b7a0f088ea7b0514bcf36
Reviewed-on: https://gerrit.libreoffice.org/51863Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>