RFR: 8367284: (fs) Support current working directory target in SecureDirectoryStream.move [v2]

[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.

Brian Burkhalter has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - 8367284: Update targetdir param verbiage to allow null
 - Merge
 - 8367284: Update test after all
 - 8367284: (fs) Support current working directory target in SecureDirectoryStream.move

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27178/files
  - new: https://git.openjdk.org/jdk/pull/27178/files/5eeb5873..7c21d87e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27178&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27178&range=00-01

  Stats: 639253 lines in 8209 files changed: 433573 ins; 122979 del; 82701 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