RFR: 8252971: WindowsFileAttributes does not know about Unix domain sockets [v4]

[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

Michael McMahon 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 11 additional commits since the last revision:

 - Merge branch 'master' into 8252971-socket-attributes
 - add specific check for unix domain socket
 - Merge branch 'master' into 8252971-socket-attributes
 - update
 - update
 - update
 - update
 - update after Alan's first review
 - Merge branch 'master' into 8252971-socket-attributes
 - test update
 - ... and 1 more: https://git.openjdk.java.net/jdk/compare/fa59fe8c...746b4762

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2424/files
  - new: https://git.openjdk.java.net/jdk/pull/2424/files/de2a3428..746b4762

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2424&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2424&range=02-03

  Stats: 2471 lines in 59 files changed: 1349 ins; 861 del; 261 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