snowflake column identifier for copy into / query data staged in files

According to documentation, Snowflake allows:
* [query data staged in files](https://docs.snowflake.com/en/user-guide/querying-stage.html#required-parameters) with an identifier of a form `[.]$[.]`
* [copy into table](https://docs.snowflake.com/en/user-guide/data-load-transform.html) with an column identifier containing `$` character like `select t.$1,t.$2,t.$3 from @~/datafile.csv.gz t;`

Although the feature seems to be snowflake specific, it cannot be implemented within snowflake dialect. It's because tokens starting with `$` character are tokenized into `Token::Placeholder`. That's why parser's change is required.

Initial OpenLineage project issue: https://github.com/OpenLineage/OpenLineage/issues/814

從 lexer 和 parser 著手，檢查以 `$` 開頭的 token 處理方式，尤其是目前會產生 `Token::Placeholder` 的路徑，並檢視 Snowflake 方言的處理。只要文件中所述的 staged-file 和 COPY INTO 欄位形式能正確解析，且不會造成現有 placeholder 語法回歸，工作就完成了。

由索引模型根據 Issue 內容生成。