RFR: 8339574: Behavior of File.is{Directory,File,Hidden} is not documented with respect to symlinks

[Brian Burkhalter]

Make explicit how the `java.io.File` methods `isDirectory`, `isFile`, and `isHidden` behave when the `File` represents a symbolic link.

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Commit messages:
 - 8339574: Behavior of File.is{Directory,File,Hidden} is not documented with respect to symlinks

Changes: https://git.openjdk.org/jdk/pull/20878/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20878&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339574
  Stats: 9 lines in 1 file changed: 5 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/20878.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20878/head:pull/20878

PR: https://git.openjdk.org/jdk/pull/20878