Tracking issue: skip attributes

[nrc]

RFC 2103 will let us use #[rustfmt::skip] without a warning.

• merge RFC 2103 (nrc)
• implement the new scoped attributes in Rust
• recognise the scoped attributes in rustfmt
• document and recommend the new attributes
• stabilise the new attributes in Rust
• deprecate the old attributes

[nrc]

There is an implementation at rust-lang/rust#47773 but it needs a test fixing and a rebase.

[nrc]

See rust-lang/rust#51277 which is a bug in the scoped attributes implementation.

[nrc]

Update still blocked on FCP and fixing 51277. I've pinged people...

[topecongiro]

rust-lang/rust#51277 is closed 🙌