The 'set' datatype in Python does not provide iteration-order
guarantees related to insertion-order. That means that its
usage in the 'split_csv' helper function during documentation
build can produce nondeterministic results.
That is non-desirable for two reasons: it means that the
documentation output may appear to vary unnecessarily between
builds, and secondly there could be loss-of-information in cases
where tag order in the source documentation is significant.
This patch implements order-preserving de-duplication of tags,
allowing authors to specify tags using intentional priority
ordering, while also removing tags that appear more than once.
(cherry picked from commit 5a79b36f56)
3ecef74b9a