Is your feature request related to a problem or challenge?

The current implementation in #9936 for Sort is probably not correct.
It ignores asc and null_first field.
IMO, the better struct for Sort and order_by is OrderByExpr
https://github.com/sqlparser-rs/sqlparser-rs/blob/deaa6d8151c8f90a7e9cbb624876fe0e8b8a165d/src/ast/query.rs#L1444-L1450
However, OrderByExpr is not an enum item in Expr

Describe the solution you'd like

two steps:

1. make OrderByExpr an enum in Expr (change in sql-parser)
2. make Sort return a OrderByExpr during Expr->String

Describe alternatives you've considered

No response

Additional context

No response