RFR: 8338696: (fs) BasicFileAttributes.creationTime() falls back to epoch if birth time is unavailable (Linux)

[Brian Burkhalter]

Set the value returned by `BasicFileAttributes.creationTime()` on Linux to the birth time, if available, otherwise return the last modified time.

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Commit messages:
 - 8338696: (fs) BasicFileAttributes.creationTime() falls back to epoch if birth time is unavailable (Linux)

Changes: https://git.openjdk.org/jdk/pull/20655/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20655&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338696
  Stats: 25 lines in 1 file changed: 16 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/20655.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20655/head:pull/20655

PR: https://git.openjdk.org/jdk/pull/20655