RFR: 8356036: Use Long::hashCode in sun.nio

[Shaojin Wen]

Similar to #24959 and #24971, sun.nio.ch.FileKey/sun.nio.fs.UnixFileKey/sun.nio.fs.UnixFileStore in java.base can also be simplified similarly.

Replace manual bitwise operations in hashCode implementations of sun.nio.ch.FileKey/sun.nio.fs.UnixFileKey/sun.nio.fs.UnixFileStore with Long::hashCode.

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Commit messages:
 - Use Long::hashCode

Changes: https://git.openjdk.org/jdk/pull/24987/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24987&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356036
  Stats: 5 lines in 3 files changed: 0 ins; 2 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/24987.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24987/head:pull/24987

PR: https://git.openjdk.org/jdk/pull/24987