RFR: 8295753: (fs) UnixPath::toRealPath does not return correct case when links not followed [v3]

[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.

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

  8295753: Clean up UnixPath; rename retentive to preserving

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10843/files
  - new: https://git.openjdk.org/jdk/pull/10843/files/96c0257a..49d18c6a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10843&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10843&range=01-02

  Stats: 43 lines in 3 files changed: 11 ins; 18 del; 14 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