Can't evaluate `CREATE TABLE` with `INDEX` in MySQL

`sqlparser-rs` couldn't evaluate following MySQL statement.

```mysql
CREATE TABLE users (id INT, name VARCHAR(10), INDEX (id));
```

Evaluating this statement by using cli caused following error.

```
[nannany@nannanynoMBP sqlparser-rs (main %=)]$ cargo run --example cli create_table.sql --mysql
Finished dev [unoptimized + debuginfo] target(s) in 0.02s
Running `target/debug/examples/cli create_table.sql --mysql`
Parsing from file 'create_table.sql' using MySqlDialect
2022-04-17T07:36:14.347Z DEBUG [sqlparser::parser] Parsing sql 'CREATE TABLE users (id INT, name VARCHAR(10), INDEX (id));
'...
Error during parsing: ParserError("Expected a data type name, found: (")
```

I tried version 0.16.0.

首先，使用 MySqlDialect 和提供的 create_table.sql 输入，通过 CLI 示例复现该语句。跟踪表级 INDEX 子句的解析器错误，然后为此 MySQL 语句添加覆盖测试，并验证它能够成功解析，且不会导致其他 CREATE TABLE 形式发生回归。

由索引模型根据 Issue 内容生成。