Use identifiable structs for AST variant fields

When consuming the generated AST for further processing, one needs to match against and deconstruct `ast::Statement` instances. Currently, the fields of this enum's variants are defined inline... which makes it impossible for downstream code to represent the nested structures as types. For example, consider this structure:

https://github.com/ballista-compute/sqlparser-rs/blob/35ef0eee3857c59827b2587bc813218a00dce264/src/ast/mod.rs#L490-L497

I propose we migrate to the following pattern.
```rust
pub struct AnalyzeStatement {
table_name: ObjectName,
partitions: Option>,
for_columns: bool,
....
}
pub enum Statement {
Analyze(AnalyzeStatement),
...
}
```

Obviously this is a massive breaking change, but that seems OK given the `0.9.x` crates.io version.

Thoughts?

Comienza revisando el enum Statement y las definiciones relacionadas en src/ast/mod.rs, especialmente las líneas enlazadas alrededor de 490-497. Evalúa cómo cada campo inline de una variante podría convertirse en una estructura identificable, preservando la forma propuesta del AST. Se considera terminado cuando las variantes relevantes del AST utilizan estructuras con nombre y el cambio de API incompatible resultante se aplica de forma coherente.

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