format_ident! does not support spans with capturing format strings

`format_ident!` seems to support the new capturing format strings introduced in Rust 1.58 on first glance. However, `format_ident!("{name}")` with a captured variable `name: Ident` produces an `Ident` with `Span::call_site()`, whereas `format_ident!("{}", name)` produces an `Ident` that keeps the span of `name`.