Plain `readdir` is preferred and while not (yet) specified in POSIX it is thread-safe for different directory streams in popular implementations.
PiperOrigin-RevId: 423321528
Change-Id: I4e1e842f338ff7d690c36e7f699b2f3637609524
This change should make it less confusing where utility code comes from.
Having it in two places made sense when we were debating whether to publish
Sandbox2 separately, but not any longer.
Follow-up changes will move `sandbox2/util.h` and rename the remaining
`sandbox2/util` folder.
PiperOrigin-RevId: 351601640
Change-Id: I6256845261f610e590c25e2c59851cc51da2d778
