Support rename columns interchangeably

[tangenta]

Enhancement

create table t (a int, b int);
alter table t rename column a to b, rename column b to a;

Expected:

Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

But got:

ERROR 1060 (42S21): Duplicate column name 'b'