`SHOW CREATE TABLE` and `Restore` of column default expressions should be enclosed within parentheses

[CbcWestwolf]

Bug Report

In the following result of SHOW CREATE TABLE, the output of rand() should be enclosed within parentheses like MySQL.

1. Minimal reproduce step (Required)

create table t (a float default (rand()));
show create table t\G

2. What did you expect to see? (Required)

***************************[ 1. row ]***************************
Table        | t
Create Table | CREATE TABLE `t` (
  `a` float DEFAULT (rand())
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci

3. What did you see instead (Required)

*************************** 1. row ***************************
       Table: t
Create Table: CREATE TABLE `t` (
  `a` float DEFAULT rand()
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin

4. What is your TiDB version? (Required)

TiDB 6.1.0 ~ master