Fix `csv_query_approx_count` once binary type coercion PR is merged

**Describe the bug**

`csv_query_approx_count` fails due to an edge case exposed in https://github.com/apache/arrow-datafusion/pull/3222

The test fails with:

```
"Plan(\"Aggregations require unique expression names but the expression \\\"APPROXDISTINCT(#aggregate_test_100.c9)\\\" at position 0 and \\\"APPROXDISTINCT(CAST(#aggregate_test_100.c9 AS Utf8))\\\" at position 1 have the same name. Consider aliasing (\\\"AS\\\") one of them.\")
```

However, the expressions are already aliased. The alias is dropped before the error check above and this part of the codebase needs some reworking. It is not trivial to fix.

**To Reproduce**

```
#[tokio::test]
async fn csv_query_approx_count() -> Result<()> {
let ctx = SessionContext::new();
register_aggregate_csv(&ctx).await?;
let sql = "SELECT approx_distinct(c9) count_c9, approx_distinct(cast(c9 as varchar)) count_c9_str FROM aggregate_test_100";
let actual = execute_to_batches(&ctx, sql).await;
let expected = vec![
"+----------+--------------+",
"| count_c9 | count_c9_str |",
"+----------+--------------+",
"| 100 | 99 |",
"+----------+--------------+",
];
assert_batches_eq!(expected, &actual);
Ok(())
}
```

**Expected behavior**
Should pass

**Additional context**
None

Inizia con il riproduttore csv_query_approx_count, includendo register_aggregate_csv, execute_to_batches e l'errore di aggregazione mostrato nell'issue. Traccia dove vengono gestiti gli alias prima del controllo delle espressioni duplicate, quindi conferma che la query produca i risultati attesi 100 e 99 quando sarà disponibile la modifica per la coercizione dei tipi binari.

Scritto dal modello di indicizzazione a partire dal testo della issue.