Auto merge of #124157 - wutchzone:partial_eq, r=estebank

Do not add leading asterisk in the `PartialEq`

I think we should address this issue, however I am not exactly sure, if this is the right way to do it. It is related to the #123056.

Imagine the simplified code:

```rust
trait MyTrait {}

impl PartialEq for dyn MyTrait {
    fn eq(&self, _other: &Self) -> bool {
        true
    }
}

#[derive(PartialEq)]
enum Bar {
    Foo(Box<dyn MyTrait>),
}
```

On the nightly compiler, the `derive` produces invalid code with the weird error message:
```
error[E0507]: cannot move out of `*__arg1_0` which is behind a shared reference
  --> src/main.rs:11:9
   |
9  | #[derive(PartialEq)]
   |          --------- in this derive macro expansion
10 | enum Things {
11 |     Foo(Box<dyn MyTrait>),
   |         ^^^^^^^^^^^^^^^^ move occurs because `*__arg1_0` has type `Box<dyn MyTrait>`, which does not implement the `Copy` trait
   |
   = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
```

It may be related to the perfect derive problem, although requiring the _type_ to be `Copy` seems unfortunate because it is not necessary. Besides, we are adding the extra dereference only for the diagnostics?

Author: bors