Can't parse valid Snowflake compound expression

Hey there, thanks for the great project!

I'm encountering an issue with the following query, which is valid in Snowflake:

```sql
SELECT v.$2 FROM (VALUES (1, 'value1'), (2, 'value2')) AS v
```

It can't get parsed with sqlparser-rs:

```
Expected: an identifier or a '*' after '.', found: $2 at Line: 1, Column: 10
```

While this syntax isn't valid in PostgreSQL, it is accepted by Snowflake. `SELECT $2 FROM ...` (without the alias) parses correctly, so it seems the parser has trouble with positional parameters when they're part of compound expressions.

Is this a gap in the Snowflake dialect implementation?

Comienza reproduciendo la consulta de Snowflake `SELECT v.$2 FROM (VALUES (1, 'value1'), (2, 'value2')) AS v` en el manejo del dialecto Snowflake del parser. Rastrea cómo las expresiones compuestas procesan el parámetro posicional `$2` después de un alias. Se considera terminado cuando esta expresión válida de Snowflake se analiza correctamente sin introducir regresiones en el caso existente `SELECT $2 FROM ...`.

Escrito por el modelo de indexación a partir del texto del issue.