pgsql: In pg_dump, avoid doing per-table queries for RLS policies.

In pg_dump, avoid doing per-table queries for RLS policies.

For no particularly good reason, getPolicies() queried pg_policy
separately for each table. We can collect all the policies in
a single query instead, and attach them to the correct TableInfo
objects using findTableByOid() lookups. On the regression
database, this reduces the number of queries substantially, and
provides a visible savings even when running against a local
server.

Per complaint from Hubert Depesz Lubaczewski. Since this is such
a simple fix and can have a visible performance benefit, back-patch
to all supported branches.

Discussion: https://postgr.es/m/20210826084430.GA26282@depesz.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/bd3611db5a6f3726094872f59feab426374d2c46

Modified Files
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src/bin/pg_dump/pg_dump.c | 92 ++++++++++++++++++++++-------------------------
1 file changed, 42 insertions(+), 50 deletions(-)