Support utf8mb4_0900_ai_ci when new collation is enabled

[GMHDBJD]

Feature Request

Is your feature request related to a problem? Please describe:

create database and show create database in mysql 8.0.23

mysql> create database db;
Query OK, 1 row affected (0.02 sec)

mysql> show create database db;
+----------+------------------------------------------------------------------------------------------------------------------------------+
| Database | Create Database                                                                                                              |
+----------+------------------------------------------------------------------------------------------------------------------------------+
| db       | CREATE DATABASE `db` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci */ /*!80016 DEFAULT ENCRYPTION='N' */ |
+----------+------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

then create database in tidb v6.x

mysql> CREATE DATABASE `db` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci */ /*!80016 DEFAULT ENCRYPTION='N' */;
ERROR 1273 (HY000): Unsupported collation when new collation is enabled: 'utf8mb4_0900_ai_ci'

Describe the feature you'd like:

support utf9mb4_0900_ai_ci

Describe alternatives you've considered:

align utf8mb4_0900_ai_ci as utf8mb4_general_ci

Teachability, Documentation, Adoption, Migration Strategy:

[mikechengwei]

/assign