fix decimal output

[daviszhen]

What type of PR is this?

• API-change
• BUG
• Improvement
• Documentation
• Feature
• Test and CI
• Code Refactoring

Which issue(s) this PR fixes:

issue #https://github.com/matrixorigin/MO-Cloud/issues/4318

https://github.com/matrixorigin/MO-Cloud/issues/4321

What this PR does / why we need it:

1, show columns(desc) 中decimal类型增加精度。

修改前：

mysql> desc tb_1;                                                                                                    
+-------+-------------+------+------+---------+-------+---------+
| Field | Type        | Null | Key  | Default | Extra | Comment |
+-------+-------------+------+------+---------+-------+---------+
| c1    | DECIMAL(15) | YES  |      | NULL    |       |         |                                                
| c2    | INT(32)     | YES  |      | NULL    |       |         |                                                
+-------+-------------+------+------+---------+-------+---------+    

修改后：

mysql> desc tb_1;                                          
+-------+---------------+------+------+---------+-------+---------+
| Field | Type          | Null | Key  | Default | Extra | Comment |
+-------+---------------+------+------+---------+-------+---------+
| c1    | DECIMAL(15,2) | YES  |      | NULL    |       |         |
| c2    | INT(32)       | YES  |      | NULL    |       |         |
+-------+---------------+------+------+---------+-------+---------+

2, cherry-pick show columns（desc）兼容性问题。

原因：mysql 中default值，show columns（desc）与show create table的展示结果是不同的。

mysql的结果

mysql> show create table t1;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                            |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t1    | CREATE TABLE `t1` (
  `a` varchar(100) DEFAULT 'abc',
  `b` char(1) DEFAULT '0',
  `c` varchar(100) DEFAULT 'abc''d'
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show full columns from t1;
+-------+--------------+--------------------+------+-----+---------+-------+---------------------------------+---------+
| Field | Type         | Collation          | Null | Key | Default | Extra | Privileges                      | Comment |
+-------+--------------+--------------------+------+-----+---------+-------+---------------------------------+---------+
| a     | varchar(100) | utf8mb4_0900_ai_ci | YES  |     | abc     |       | select,insert,update,references |         |
| b     | char(1)      | utf8mb4_0900_ai_ci | YES  |     | 0       |       | select,insert,update,references |         |
| c     | varchar(100) | utf8mb4_0900_ai_ci | YES  |     | abc'd   |       | select,insert,update,references |         |
+-------+--------------+--------------------+------+-----+---------+-------+---------------------------------+---------+
3 rows in set (0.00 sec)

修改：区分show columns（desc）与show create table的default值