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

Inizia leggendo la sezione collegata del tokenizer in src/tokenizer.rs e gli esempi di gestione degli spazi bianchi in src/parser/mod.rs. Segui il percorso dei token di spazi bianchi dalla tokenizzazione al filtraggio del parser, quindi esamina i test correlati del parser, se presenti. Il lavoro è completato quando il refactor proposto per la gestione degli spazi bianchi è definito in modo coerente e il comportamento del parser continua a essere coperto.

Scritto dal modello di indicizzazione a partire dal testo della issue.