Compatibility: support ALTER TABLE... PARTITION BY

[shlomi-noach]

Our parser today does not support ALTER TABLE ... PARTITION BY. It does support statements like ALTER TABLE ... ADD PARTITION or ALTER TABLE.... REORGANIZE PARTITION etc. But is missing on the "completely repartition like so" option.

Example query:

ALTER TABLE t PARTITION BY HASH(id) PARTITIONS 4;

MySQL's ALTER TABLE lets you repartition everything according to a completely new scheme. Basically, it uses the same partitioning syntax from CREATE TABLE. We already have this supported in CREATE TABLE in the form of PartitionOption

All we need to do to close this issue is to support PartitionOption inside AlterTable

Self assigning

[shlomi-noach]

Related: #8604

There is at least another outstanding partitioning limitation to the parser; in #8604 partitioning is marked as complete but I believe that's a mistake.