Use `Ident::parse_any` for `name` attributes

[Databean]

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:

An identifier constructed with Ident::new is permitted to be a Rust keyword, though parsing one through its Parse implementation rejects Rust keywords. Use input.call(Ident::parse_any) when parsing to match the behaviour of Ident::new.

Fixes issue #4225

[adamreichold]

Could you please add your example as a test case so that we do not regress on this in the future? Thank!

(It would be nice if it covered as many places as possible, e.g. functions, methods, properties, etc.)

[Databean]

Added test cases and a newsfragments entry.