instead of copying them to a new data structure that
is practically identical.
Helps startup time since we build a ton of these when
loading documents.
And use o3tl::sorted_vector as a dense map data
structure to reduce allocations and improve cache
friendliness, since this is a build-once thing.
Change-Id: I950be03b1a21c0c81c40f2677d4215f5e8e256cf
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/114015
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>