ast: provider builders for convenient programmatic construction

I have a use case where I'm generating SQL strings, and in general having `sqlparser::ast` is quite good, but the structs are particularly painful to construct programatically. It'd be interesting if the ast structs offered an optional feature that had https://github.com/elastio/bon builders derived to build them.

Maybe somebody will teach me how to safely construct strings that I can then parse (that'd be fine! I just am not generally eager to be doing string formatting to produce sql, particularly given I don't have full control over the identifiers). For now I am generally just doing this formatting, but I don't love it.

A issue aponta sqlparser::ast e uma feature opcional de builder derivada de bon como pontos de entrada; inspecione como as estruturas AST e as features opcionais estão definidas atualmente. O resultado deve ser uma abordagem de builder acordada e utilizável para as estruturas AST relevantes, reduzindo a necessidade de formatar strings SQL manualmente.

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