std::multiset seems to be pretty slow to construct and
destruct, even if we ~never put anything into these listener
lists, so rather use o3tl::sorted_vector, which has more
predictable performance.
Shaves 10% off startup time for me.
Change-Id: I13afcbe3cb63522e4efe61c64f773e1ffbec9683
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/167101
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
