MSSQL: Issue with CTE anchors

Hi, the following is a valid MSSQL syntax

When parsed with the `sql-parser-rs`

```sql
WITH RecursiveCTE AS (
-- Anchor member
SELECT TOP 1
[ID],
CAST([Amount] AS NUMERIC) AS [Amount],
CAST([Balance] AS NUMERIC) AS [Balance],
(SELECT TOP 1 [FixedValue] FROM [Settings] ORDER BY [ID] DESC) AS [Constant]
FROM [Transactions]
ORDER BY [ID] ASC

UNION ALL

-- Recursive member
SELECT
[ID] + 1 AS [ID],
CAST([Amount] * 0.8 AS NUMERIC) AS [Amount],
CAST(([Amount] * 0.8 - [Constant]) AS NUMERIC) AS [Balance],
[Constant]
FROM RecursiveCTE
WHERE [Balance] > 0
)
SELECT [ID], [Balance]
FROM RecursiveCTE
ORDER BY [ID] ASC;
```

it gives the following error

```bash
sql parser error: Expected: ), found: UNION at Line: 11, Column: 5
```

https://learn.microsoft.com/en-us/sql/t-sql/queries/with-common-table-expression-transact-sql

Inizia riproducendo la query CTE MSSQL fornita in sql-parser-rs e confronta la gestione delle CTE da parte del parser con la documentazione Microsoft collegata. Segui il punto di ingresso del parser che segnala unexpected UNION, quindi aggiungi un test di regressione che dimostri che la query viene analizzata correttamente.

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