PSA: rustfmt is moving

[Tyler Mandry]

If you don't write Rust you can stop reading now.

tl;dr: Previously our editor configuration docs told people to point to the rustfmt binary in //prebuilt/third_party/rust_tools. If you have this configured, you'll need to replace rust_tools with rust in the path.

If you have rustup installed, check that any custom rustup toolchains you have configured point to rust and not rust_tools. You can use rustup toolchain list -v to see this and rustup toolchain link to update the path.

rust_tools is a prebuilt package that shipped tools like rustfmt and clippy that historically broke a lot because they lived out of the main Rust tree. Rust has now solved this problem using git subtree. This means we can now remove gigabytes of unnecessary prebuilt bloat and while streamlining our workflow for toolchain maintenance!

It also means you may need to update your dev environment (see above). rust_tools will stick around for 1-2 weeks to give people time to make this transition. If you need more time for some reason, please let me know.

P.S. This will mean that we will no longer ship miri, the last holdout for git subtree, at least until it catches up with the other tools. To my knowledge miri is very rarely if ever used in our tree. If you're relying on miri for something, please let me know!