RFR: 8337124: (fs) sun.nio.fs.WindowsSecurity.enablePrivilege should pin when continuations supported

[Brian Burkhalter]

In `sun.nio.fs.WindowsSecurity.enablePrivilege`, change `PreviewFeatures.isEnabled` to `ContinuationSupport.isSupported`.

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Commit messages:
 - 8337124: (fs) sun.nio.fs.WindowsSecurity.enablePrivilege should pin when continuations supported

Changes: https://git.openjdk.org/jdk/pull/20319/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20319&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337124
  Stats: 5 lines in 1 file changed: 1 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/20319.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20319/head:pull/20319

PR: https://git.openjdk.org/jdk/pull/20319