if we create the list every time we call
ViewContact::getViewIndependentPrimitive2DContainer
then caching the result is rather worthless.
So make the caching worthwhile, which means invalidating
it when something changes.
Change-Id: I081e9501255ec1c87454bfcc1e0a741109afa99f
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/113891
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
44711d9eb5