Upstream Rust maintenance report

As noted in my previous report, I am currently working on the open source Rust toolchain as a Sovereign Tech Fellow. Every two months, I’m putting out a report of my open source work done in that period. This is the second installment of this series. Same as the last time, I’ll try to pick a few highlights, summarize the rest of the stuff that I worked on, and also provide contribution statistics and a raw list of opened PRs.