pgsql: Fix per-tuple memory leak in partition tuple routing

Fix per-tuple memory leak in partition tuple routing

Some operations were being done in a longer-lived memory context,
causing intra-query leaks. It's not noticeable unless you're doing a
large COPY, but if you are, it eats enough memory to cause a problem.

Co-authored-by: Kohei KaiGai <kaigai(at)heterodb(dot)com>
Co-authored-by: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
Co-authored-by: Álvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Discussion: https://postgr.es/m/CAOP8fzYtVFWZADq4c=KoTAqgDrHWfng+AnEPEZccyxqxPVbbWQ@mail.gmail.com

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/34295b87fbbcbaf26280f53f006b20971dbad1f3

Modified Files
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src/backend/executor/execPartition.c | 52 ++++++++++++++++++++++++++----------
1 file changed, 38 insertions(+), 14 deletions(-)