Rollup merge of #99337 - jsha:simplify-highlight, r=GuillaumeGomez

rustdoc: simplify highlight.rs

Split render_with_highlighting, which took many optional parameters, into three functions for specific purposes, which each take a smaller number of mostly required parameters.

Remove some plumbing to pass through an "edition" parameter, which was used solely to avoid highlighting some 2021 Edition keywords in non-2021 code.

I've tested a build of std docs before and after, and this does not change the generated HTML at all.

Followup from rust-lang/rust#91264 (comment)

r? ``@GuillaumeGomez``