RFR: 8276661: (fs) UserDefinedFileAttributeView no longer works with long path (win)

[Brian Burkhalter]

Please consider this change which uses a new method `WindowsPath::getPathWithPrefixForWin32Calls`.

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Commit messages:
 - 8276661: (fs) UserDefinedFileAttributeView no longer works with long path (win)

Changes: https://git.openjdk.java.net/jdk/pull/6435/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6435&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276661
  Stats: 32 lines in 3 files changed: 23 ins; 2 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6435.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6435/head:pull/6435

PR: https://git.openjdk.java.net/jdk/pull/6435