Problem:
When a partition table is in-place altered to add an auto-increment column,
then its values are starting over for each partition.

Analysis:
In the case of in-place alter, InnoDB is creating a new sequence object
for each partition. It is default initialized. So auto-increment columns
start over for each partition.

Fix:
Assign old sequence of the partition to the sequence of next partition
so it won't start over.

RB#21148
Reviewed by Bin Su <bin.x.su@oracle.com>