instead of returning a Primitive2DContainer from each method which we
are then going to immediately append to another container, pass down a
single container by reference which we can append to

Change-Id: I0f28a499d2ec54f7111a7044c30099767aa079e1
Reviewed-on: https://gerrit.libreoffice.org/30258Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>