improve performance of pg_dump with many sequences

Similar to 'pg_dump --binary-upgrade' [0], we can speed up pg_dump with
many sequences by gathering the required information in a single query
instead of two queries per sequence. The attached patches are
works-in-progress, but here are the results I see on my machine for
'pg_dump --schema-only --binary-upgrade' with a million sequences:

HEAD : 6m22.809s
[0] : 1m54.701s
[0] + attached : 0m38.233s

I'm not sure I have all the details correct in 0003, and we might want to
separate the table into two tables which are only populated when the
relevant section is dumped. Furthermore, the query in 0003 is a bit goofy
because it needs to dance around a bug reported elsewhere [1].

[0] https://postgr.es/m/20240418041712.GA3441570%40nathanxps13
[1] https://postgr.es/m/20240501005730.GA594666%40nathanxps13

--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com