parser: Support alter convert to syntax

[spongedu]

for #6394.
This PR support the ALTER TABLE CONVERT TO CHARACTER SET charset_name [COLLATE collation_name] syntax, but not actually change the charset or collation. That's because for now, nothing is done when change character set or collation in ALTER TABLE statements in TiDB, the related TableOption are ignored in function AlterTable in ddl/ddl_api.go.
For example:
In MySQL

mysql> create table t1 (a tinytext character set latin1);                                                                                    
Query OK, 0 rows affected (0.03 sec)

mysql> show create table t1;
+-------+---------------------------------------------------------------------------+
| Table | Create Table                                                              |
+-------+---------------------------------------------------------------------------+
| t1    | CREATE TABLE `t1` (
  `a` tinytext
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+---------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> alter table t1 default character set utf8;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table t1;                                                                                                                 
+-------+----------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                 |
+-------+----------------------------------------------------------------------------------------------+
| t1    | CREATE TABLE `t1` (
  `a` tinytext CHARACTER SET latin1
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+----------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> alter table t1 default collate latin1_bin;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table t1;                                                                                                                 
+-------+-------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                      |
+-------+-------------------------------------------------------------------------------------------------------------------+
| t1    | CREATE TABLE `t1` (
  `a` tinytext CHARACTER SET latin1
) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_bin |
+-------+-------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

In TiDB:

tidb> create table t1 (a tinytext character set latin1);
Query OK, 0 rows affected (0.01 sec)

tidb> show create table t1;                                                                                                                  +-------+-------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                          |
+-------+-------------------------------------------------------------------------------------------------------+
| t1    | CREATE TABLE `t1` (
  `a` tinytext DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin |
+-------+-------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

tidb>                                                                                                                                        tidb> alter table t1 default character set latin1;
Query OK, 0 rows affected (0.00 sec)

tidb> show create table t1;                                                                                                                  +-------+-------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                          |
+-------+-------------------------------------------------------------------------------------------------------+
| t1    | CREATE TABLE `t1` (
  `a` tinytext DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin |
+-------+-------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

tidb> alter table t1 default collate latin1_bin;
Query OK, 0 rows affected (0.00 sec)

tidb> show create table t1;                                                                                                                  
+-------+-------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                          |
+-------+-------------------------------------------------------------------------------------------------------+
| t1    | CREATE TABLE `t1` (
  `a` tinytext DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin |
+-------+-------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

Maybe we should fix this in another PR.

[zz-jason]

LGTM

[zz-jason]

@spongedu maybe we can just return a warning to client, this is easier than supporting another collate.

[coocood]

LGTM

[coocood]

/run-all-tests