Add ergonomic ref counting support

[spastorino]

Opening this to keep track of ergonomic ref-counting. We need to add support for .use and use closures. This is an experimental nightly feature landed in rust-lang/rust#134797

[ytmimi]

Given that the proposed syntax is x.use we probably want to support this the same way we already handle chains. You can take a look at what's been started in rust-lang/rust#138435 for postfix yields. I suspect that we'll handle .use similar to .yield and .await.

We haven't synced the r-l/r changes back into rustfmt yet, so if you or someone else works on implementing this formatting I'd be happy to review a PR here or in the r-l/r tree.

[spastorino]

There's .use which would be similiar to .yield and .await but there's also use closures use || { ... }, which would be similar to move || { ... }. I can try to take a look at this at some point if nobody beats me.

[ytmimi]

@spastorino I think this should do it: #6532