The dprint formatter is a flexible system which will use sandboxed
WebAssembly formatters to format our code (mostly: it calls out to
`rustfmt` for Rust code).
A particularly interesting feature is that dprint can format Rust code
blocks in the Markdown files. However, before we turn that on, we need
to have a way to normalize the Markdown text as it is extracted[1].
That is so that the word put into the translations is kept after the
reformatting.
[1]: https://github.com/google/mdbook-i18n-helpers/issues/19
This requires us to run a nightly Rust for our formatting check[1]. Other
users will see a warning when invoking `rustfmt`:
Warning: can't set `imports_granularity = Module`, unstable features
are only available in nightly channel.
This should be harmless overall and help us ensure better consistency
in our import formatting.
[1]: https://rust-lang.github.io/rustfmt/?version=v1.5.1&search=#imports_granularity