Auto merge of #135494 - yotamofek:rustdoc-fmt-from_fn, r=fmease

Refactor `fmt::Display` impls in rustdoc

This PR does a couple of things, with the intention of cleaning up and streamlining some of the `fmt::Display` impls in rustdoc:
1. Use the unstable [`fmt::from_fn`](rust-lang/rust#117729) instead of open-coding it.
2. ~~Replace bespoke implementations of `Itertools::format` with the method itself.~~
4. Some more minor cleanups - DRY, remove unnecessary calls to `Symbol::as_str()`, replace some `format!()` calls with lazier options

The changes are mostly cosmetic but some of them might have a slight positive effect on performance.

Author: bors