Add #![feature(ergonomic_clones)] formatting

[ytmimi]

Tracking issue rust-lang/rust#134797

Closes #6512

[ytmimi]

@spastorino thanks for taking a look at the implementation. I'll go ahead and get this merged now and the formatting will be available in r-l/rust after the next subtree sync, which I hope to get out soon(ish).

[spastorino]

@spastorino thanks for taking a look at the implementation. I'll go ahead and get this merged now and the formatting will be available in r-l/rust after the next subtree sync, which I hope to get out soon(ish).

I've opened this rust-lang/rust#139692, not sure when this change is going to be used in rust-lang/rust's rustfmt. Please let me know when the sync happens so I can rebase the PR and mark it as ready.

[spastorino]

@ytmimi I didn't do a proper check to be honest, but I was surprised that this is not yet included in rustfmt 1.8.0-nightly (ce7e97f737 2025-05-11).