Eliminating whitespace from the parser logic

Hi,

At this time, whitespace tokens are stored in the parser, and are then filtered out in several distinct points in the parser logic, such as:

* https://github.com/apache/datafusion-sqlparser-rs/blob/67684c84d4c2589356c411ea4917dcf1defcd77c/src/parser/mod.rs#L4032-L4049
* https://github.com/apache/datafusion-sqlparser-rs/blob/67684c84d4c2589356c411ea4917dcf1defcd77c/src/parser/mod.rs#L4055-L4069
* https://github.com/apache/datafusion-sqlparser-rs/blob/67684c84d4c2589356c411ea4917dcf1defcd77c/src/parser/mod.rs#L4077-L4094
* https://github.com/apache/datafusion-sqlparser-rs/blob/67684c84d4c2589356c411ea4917dcf1defcd77c/src/parser/mod.rs#L4149-L4160
* https://github.com/apache/datafusion-sqlparser-rs/blob/67684c84d4c2589356c411ea4917dcf1defcd77c/src/parser/mod.rs#L4183-L4202

and many more.

SQL, as far as I know, is not a language that cares about spaces like Python - it should be safe to remove all concepts of whitespaces after [the tokenization process](https://github.com/apache/datafusion-sqlparser-rs/blob/67684c84d4c2589356c411ea4917dcf1defcd77c/src/tokenizer.rs#L937-L942) is complete, and this should:

* Reduce memory requirements, as whitespace tokens would not be stored anymore
* Significantly simplify parser logic by removing all of the whitespace-related logic from the parser
* Move the parser closer to a streaming logic, but that will require many more PRs

Since such a PR would require quite a bit of effort on my part, I would appreciate some feedback on it before moving forward with it.

@iffyio do you happen to have any opinion regarding such a refactoring?

Ciao,
Luca

まず、src/tokenizer.rs のリンクされた tokenizer セクションと、src/parser/mod.rs の空白処理の例を読んでください。空白トークンが tokenization から parser の filtering へどのように移動するかを追跡し、その後、見つかった場合は関連する parser テストを確認してください。提案された空白処理のリファクタリングが一貫して定義され、parser の動作が引き続きテストでカバーされていれば完了です。

索引モデルが issue の本文から書いたものです。