RFR: 8295753: (fs) UnixPath::toRealPath does not return correct case when links not followed [v2]

[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 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 three additional commits since the last revision:

 - Merge
 - 8295753: Use UnixDirectoryStream; compare UnixFileKeys; add SecurityManager
 - 8295753: (fs) UnixPath::toRealPath does not return correct case when links not followed

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10843/files
  - new: https://git.openjdk.org/jdk/pull/10843/files/1eb3912f..96c0257a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10843&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10843&range=00-01

  Stats: 142136 lines in 855 files changed: 82369 ins; 29444 del; 30323 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