- external links use markdown's []() format,
- local files are formated with backquotes,
- duplicated new lines were removed,
- unnecesary single spaces were removed,
- broken links and local paths were updated.
In 24765, we said that we supported rust stable in CodingStandardsRust.md.
But we left GettingStartedRust.md saying that we support rust nightly.
Closes 27160.
When merging the patches for #25310 the libc version requirement in
`GettingStartedRust.md` and `configure.ac` did not get updated to the
now needed 0.2.39.
