RFR: 8326897: (fs) The utility TestUtil.supportsLinks is wrongly used to check for hard link support

[Brian Burkhalter]

Add to `test/jdk/java/nio/file/TestUtil.java` the method `TestUtil.supportsHardLinks` and use it to conditionally test `Files.createLink` where appropriate in the `java/nio/file` tests.

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Commit messages:
 - 8326897: (fs) The utility TestUtil.supportsLinks is wrongly used to check for hard link support

Changes: https://git.openjdk.org/jdk/pull/18038/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18038&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326897
  Stats: 26 lines in 3 files changed: 21 ins; 1 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/18038.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18038/head:pull/18038

PR: https://git.openjdk.org/jdk/pull/18038