Cannot parse named windows with modifiers

sqlparser-rs only supports named windows that are an identifier. This is fine for queries like:

```sql
SELECT sum(salary) OVER w, avg(salary) OVER w
FROM empsalary
WINDOW w AS (PARTITION BY depname ORDER BY salary DESC);
```

However, it is insufficient for queries in at least BigQuery and MySQL where modifiers can be added to the named window in the OVER clause.

[MySQL named window example](https://dev.mysql.com/doc/refman/8.0/en/window-functions-named-windows.html)

```sql
SELECT
DISTINCT year, country,
FIRST_VALUE(year) OVER (w ORDER BY year ASC) AS first,
FIRST_VALUE(year) OVER (w ORDER BY year DESC) AS last
FROM sales
WINDOW w AS (PARTITION BY country)
```

[BigQuery named window example](https://cloud.google.com/bigquery/docs/reference/standard-sql/window-function-calls)

```sql
SELECT item, purchases, category, LAST_VALUE(item)
OVER (
item_window
ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING
) AS most_popular
FROM Produce
WINDOW item_window AS (
PARTITION BY category
ORDER BY purchases)
```

This would build upon prior to work:
- https://github.com/sqlparser-rs/sqlparser-rs/issues/867
- https://github.com/sqlparser-rs/sqlparser-rs/pull/881

Commencez par examiner comment sqlparser-rs analyse l’expression named-window dans la clause OVER, puis consultez l’issue #867 et la pull request #881 pour connaître la conception précédente. Ajoutez une couverture de parsing pour les exemples MySQL et BigQuery, et vérifiez que les named windows avec modificateurs sont acceptées sans provoquer de régression pour les named windows simples.

Rédigé par le modèle d'indexation à partir du texte de l'issue.