Add default and latest stable edition to --edition in rustc (attempt 2)
Fixes#106041
No longer leaks string like my first attempt PR, #106094 - uses LazyLock to construct a `&'static str`
It will now output the default edition and latest stable edition in the help message for the `--edition` flag.
Going to request the same reviewer as the first attempt for continuity - r? `@Nilstrieb`