pgsql: pg_dump: avoid unsafe function calls in getPolicies().

pg_dump: avoid unsafe function calls in getPolicies().

getPolicies() had the same disease I fixed in other places in
commit e3fcbbd62, i.e., it was calling pg_get_expr() for
expressions on tables that we don't necessarily have lock on.
To fix, restrict the query to only collect interesting rows,
rather than doing the filtering on the client side.

Back-patch of commit 3e6e86abc.  That's been in v15/HEAD long enough
to have some confidence about it, so now let's fix the problem in
older branches.

Discussion: https://postgr.es/m/2273648.1634764485@sss.pgh.pa.us
Discussion: https://postgr.es/m/7d7eb6128f40401d81b3b7a898b6b4de@W2012-02.nidsa.loc
Discussion: https://postgr.es/m/45c93d57-9973-248e-d2df-e02ca9af48d4@darold.net

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/03ac48549438f26b796c1f536c2b545c6c50f259

Modified Files
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src/bin/pg_dump/pg_dump.c | 42 +++++++++++++++++++++++++++++-------------
1 file changed, 29 insertions(+), 13 deletions(-)