RFR: 8276661: (fs) UserDefinedFileAttributeView no longer works with long path (win) [v4]

[Brian Burkhalter]

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

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  8276661: addPrefixIfNeeded calls addPrefix; remove UNC test

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6435/files
  - new: https://git.openjdk.java.net/jdk/pull/6435/files/bf5e3dcd..aecffaf9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6435&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6435&range=02-03

  Stats: 29 lines in 2 files changed: 0 ins; 15 del; 14 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