Avoid unnecessary relation stats query in pg_dump.

Avoid unnecessary relation stats query in pg_dump.

The few fields we need can be easily collected in getTables() and
getIndexes() and stored in RelStatsInfo.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reported-by: Andres Freund <andres@anarazel.de>
Co-authored-by: Corey Huinker <corey.huinker@gmail.com>
Co-authored-by: Jeff Davis <pgsql@j-davis.com>
Discussion: https://postgr.es/m/CADkLM=f0a43aTd88xW4xCFayEF25g-7hTrHX_WhV40HyocsUGg@mail.gmail.com