RFR: 8276661: (fs) UserDefinedFileAttributeView no longer works with long path (win) [v7]

[Brian Burkhalter]

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

Brian Burkhalter 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 seven additional commits since the last revision:

 - Merge
 - 8276661: Ensure GetFullPathName() is used
 - 8276661: Change getPathWithPrefixForWin32Calls to getPathWithPadForWin32Calls
 - 8276661: addPrefixIfNeeded calls addPrefix; remove UNC test
 - 8276661: Replace addPrefixIfAbsent() with addPrefix()
 - 8276661: Support UNC paths
 - 8276661: (fs) UserDefinedFileAttributeView no longer works with long path (win)

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6435/files
  - new: https://git.openjdk.java.net/jdk/pull/6435/files/3567e5ac..9f51bd7a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6435&range=06
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6435&range=05-06

  Stats: 75632 lines in 1379 files changed: 50644 ins; 14508 del; 10480 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