Inherit parent's AM for partition MERGE/SPLIT operations
This commit makes new partitions created by ALTER TABLE ... SPLIT PARTITION
and ALTER TABLE ... MERGE PARTITIONS commands inherit the paret table access
method.
Reported-by: Alexander Lakhin
Discussion: https://postgr.es/m/
84ada05b-be5c-473e-6d1c-
ebe5dd21b190%40gmail.com
Reviewed-by: Pavel Borisov