RFR: 8069345: (fs) FileTreeWalker throws NotDirectoryException on file junction points

[Brian Burkhalter]

Improve support for Windows directory junctions.

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Commit messages:
 - 8069345: (fs) FileTreeWalker throws NotDirectoryException on file junction points

Changes: https://git.openjdk.org/jdk/pull/21555/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21555&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8069345
  Stats: 712 lines in 7 files changed: 690 ins; 4 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/21555.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21555/head:pull/21555

PR: https://git.openjdk.org/jdk/pull/21555