Add select statement for OUTPUT parameters.

This will make the copy/paste experience more awesome since the user can now see the whole output.

Example:
Before
```sql
DECLARE @x int = 123;
EXEC dbo.SOMEPROCEDURE @x = @x OUTPUT;
---
DECLARE @x int = 123,
        @retval int;

EXEC @retval = dbo.SOMEPROCEDURE @x = @x OUTPUT;
SELECT @retval AS ReturnValue;
```

After
```sql
DECLARE @x int = 123;
EXEC dbo.SOMEPROCEDURE @x = @x OUTPUT;
SELECT @x AS x;
---
DECLARE @x int = 123,
        @retval int;

EXEC @retval = dbo.SOMEPROCEDURE @x = @x OUTPUT;
SELECT @retval AS ReturnValue, @x AS x;
```