RFR: 8368633: (fs) Path.toRealPath(NOFOLLOW_LINKS) very slow on macOS

[Brian Burkhalter]

Try to avoid checking file keys for all entries by first attempting `Path.compareTo` and `String.equalsIgnoreCase`.

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Commit messages:
 - 8368633: (fs) Path.toRealPath(NOFOLLOW_LINKS) very slow on macOS

Changes: https://git.openjdk.org/jdk/pull/27709/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27709&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368633
  Stats: 38 lines in 2 files changed: 14 ins; 3 del; 21 mod
  Patch: https://git.openjdk.org/jdk/pull/27709.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27709/head:pull/27709

PR: https://git.openjdk.org/jdk/pull/27709