pgsql: Revise API for partition_rbound_cmp/partition_rbound_datum_cmp.

Revise API for partition_rbound_cmp/partition_rbound_datum_cmp.

Instead of passing the PartitionKey, pass just the required bits of
it.  This allows these functions to be used without needing the
PartitionKey to be available, which is important for several
pending patches.

Ashutosh Bapat, reviewed by Amit Langote, with a comment tweak
by me.

Discussion: http://postgr.es/m/3d835ed1-36ab-f06d-0ce8-a76a2bbf7677@lab.ntt.co.jp
Discussion: http://postgr.es/m/b4d88995-094b-320c-b614-2282fae0bf6c@lab.ntt.co.jp

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b0229235564fbe3a9b1cc115ea738a07e274bf30

Modified Files
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src/backend/catalog/partition.c | 62 +++++++++++++++++++++++++++--------------
1 file changed, 41 insertions(+), 21 deletions(-)