pgsql: Reduce unnecessary list construction inRelationBuildPartitionDe

Reduce unnecessary list construction in RelationBuildPartitionDesc.

The 'partoids' list which was constructed by the previous version
of this code was necessarily identical to 'inhoids'.  There's no
point to duplicating the list, so avoid that.  Instead, construct
the array representation directly from the original 'inhoids' list.

Also, use an array rather than a list for 'boundspecs'.  We know
exactly how many items we need to store, so there's really no
reason to use a list.  Using an array instead reduces the number
of memory allocations we perform.

Patch by me, reviewed by Michael Paquier and Amit Langote, the
latter of whom also helped with rebasing.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7ee5f88e650619ee619f7e2854ac50ff59d0b0c7

Modified Files
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src/backend/partitioning/partbounds.c | 66 +++++++++++++++--------------------
src/backend/utils/cache/partcache.c   | 40 ++++++++++++---------
src/include/partitioning/partbounds.h |  5 ++-
3 files changed, 53 insertions(+), 58 deletions(-)