RFR: 8252971: WindowsFileAttributes does not know about Unix domain sockets

[Michael McMahon]

Could I get the following change reviewed please? It fixes a problem (in JEP380) on Windows where some file operations on Unix domain sockets were not working and led to the feature being disabled on Windows 2019 Server in JDK 16. So, the fix re-enables the feature on all versions of Windows that support it.

The test checks all the file APIs that were affected by the problem. The change touches the code that handles symbolic links in Windows (since they are implemented as NTFS reparse points, like Unix sockets), but I didn't add any specific testing in this area, as I assume the existing unit tests for NIO symbolic links should cover that. If I should add more tests here, then I can do that.

Thanks,
Michael

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Commit messages:
 - update
 - update
 - update
 - update
 - update after Alan's first review
 - Merge branch 'master' into 8252971-socket-attributes
 - test update
 - initial fix for review

Changes: https://git.openjdk.java.net/jdk/pull/2424/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2424&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252971
  Stats: 241 lines in 8 files changed: 226 ins; 9 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2424.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2424/head:pull/2424

PR: https://git.openjdk.java.net/jdk/pull/2424