RFR: 8295753: (fs) UnixPath::toRealPath does not return correct case when links not followed

[Brian Burkhalter]

On macOS, ensure that the components of the `Path` returned by `UnixPath::toRealPath` have the case retained by the file system as opposed to that of the representation present in the `UnixPath` instance.

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Commit messages:
 - 8295753: (fs) UnixPath::toRealPath does not return correct case when links not followed

Changes: https://git.openjdk.org/jdk/pull/10843/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10843&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295753
  Stats: 108 lines in 4 files changed: 93 ins; 2 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/10843.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10843/head:pull/10843

PR: https://git.openjdk.org/jdk/pull/10843