RFR: 8367284: (fs) Support current working directory target in SecureDirectoryStream.move

[Brian Burkhalter]

Change `java.nio.file.SecureDirectoryStream.move` so that, instead of throwing a `NullPointerException` if the `targetdir` parameter is `null`, it considers a non-absolute path passed via `targetpath` as being relative to the current working directory.

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Commit messages:
 - 8367284: Update test after all
 - 8367284: (fs) Support current working directory target in SecureDirectoryStream.move

Changes: https://git.openjdk.org/jdk/pull/27178/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27178&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367284
  Stats: 45 lines in 3 files changed: 28 ins; 6 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/27178.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27178/head:pull/27178

PR: https://git.openjdk.org/jdk/pull/27178