MySQL: Support SHOW FULL PROCESSLIST syntax

[jstnd]

Currently, parsing the syntax SHOW FULL PROCESSLIST with the MySQL dialect results in an error even though it's valid as seen in the documentation. This PR adds support for this syntax to the parser.

This is my first time contributing here, so please let me know if anything needs to be changed.

let ast = Parser::parse_sql(&MySqlDialect {}, "SHOW FULL PROCESSLIST");
println!("{:?}", ast); // Current: Err(ParserError("EXTENDED/FULL are not supported with this type of SHOW query"))

https://dev.mysql.com/doc/refman/8.4/en/show-processlist.html