Comment dropped between & and typename in parameter type

```
pub fn a(_: &/*'static*/()) {}
```

becomes

```
pub fn a(_: &()) {}
```

any reason why this (kind of critical) bug hasn't been fixed yet? It's almost open for a year now.

_Originally posted by @hellow554 in https://github.com/rust-lang/rustfmt/issues/2781#issuecomment-496403822_