Support window definitions with aliases 

Originally posted by @jonahgao in https://github.com/apache/datafusion/pull/15033#discussion_r2029886625:


>  Unrelated to the current fix, we should compare them using normalized names to support the following SQL

```sql
SELECT
  t1.v1,
  SUM(t1.v1) OVER W + 1
FROM
  generate_series(1, 5) AS t1(v1)
WINDOW
  w AS (ORDER BY t1.v1);
```

            