pgsql: Fix usage of palloc() in MERGE/SPLIT PARTITION(s) code

Fix usage of palloc() in MERGE/SPLIT PARTITION(s) code

f2e4cc427951 and 4b3d173629f4 implement ALTER TABLE ... MERGE/SPLIT
PARTITION(s) commands.  In several places, these commits use palloc(),
where we should use palloc_object() and palloc_array().  This commit
provides appropriate usage of palloc_object() and palloc_array().

Reported-by: Man Zeng <zengman@halodbtech.com>
Discussion: https://postgr.es/m/tencent_3661BB522D5466B33EA33666%40qq.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c5ae07a90a0f3594e5053a26f3c99b041df427d3

Modified Files
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src/backend/commands/tablecmds.c      |  6 +++---
src/backend/partitioning/partbounds.c | 12 ++++--------
2 files changed, 7 insertions(+), 11 deletions(-)