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

まず、提供された MSSQL CTE クエリを sql-parser-rs で再現し、パーサーの CTE 処理をリンク先の Microsoft ドキュメントと比較します。unexpected UNION を報告しているパーサーのエントリポイントを追跡し、その後、クエリが正常にパースされることを示すリグレッションテストを追加します。

索引モデルが issue の本文から書いたものです。