This makes it possible to use rust keywords as the name of python class
methods and standalone functions. For example:
```
struct MyClass {
}
impl MyClass {
#[new]
fn new() -> Self {
MyClass {}
}
#[pyo3(name = "struct")]
fn struct_method(&self) -> usize {
42
}
}
fn struct_function() -> usize {
42
}
```
From the [`syn::Ident`
documentation](https://docs.rs/syn/2.0.66/syn/struct.Ident.html):
> An identifier constructed with `Ident::new` is permitted to be a Rust
keyword, though parsing one through its
[`Parse`](https://docs.rs/syn/2.0.66/syn/parse/trait.Parse.html)
implementation rejects Rust keywords. Use `input.call(Ident::parse_any)`
when parsing to match the behaviour of `Ident::new`.
Fixes issue #4225
