docs: Build style guide updates
docs: Build style guide updates

- For the Bazel style guide, replace the Google-internal link with a
  link to the Bazel's public BUILD style guide.
- Update wording for the GN style section.

Change-Id: Idffa8a323ad60476421561e1859ee0728ed70255
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/77303
Reviewed-by: Keir Mierle <69344103cc60b36d6e1fbdc31ce6504b2286c646@google.com>
Commit-Queue: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed