raw identifiers #[difference(recurse)]

`#[difference(recurse)]` does not work with [raw identifiers](https://doc.rust-lang.org/rust-by-example/compatibility/raw_identifiers.html):

```rs
#[derive(Difference, Debug, Clone)]
pub struct Entity {
    #[difference(recurse)]
    pub r#type: MyType,  // r# raw
}

#[derive(Difference, Debug, Clone)]
pub struct MyType { ... }
```

Error: `error: prefix __r is unknown`