instead of fighting the fact that Sequence is intended to be immutable
getSequence() will become a little slower, but since getSequence()
is called 5k times during 'make check', while add/remove are called
3M times, I think it's safe to say mutation is dominant.
Change-Id: I23d127c93c589050d6c06c0da47871e1ebe7b52d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/86929
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
