RFR: 8317678: Fix up hashCode() for ZipFile.Source.Key

[Sean Coffey]

Fix up java.util.zip.ZipFile$Source hashCode() impl so that duplicate Source objects aren't created for the same zip file.

-------------

Commit messages:
 - Initial changes

Changes: https://git.openjdk.org/jdk/pull/16115/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16115&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317678
  Stats: 133 lines in 2 files changed: 131 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16115.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16115/head:pull/16115

PR: https://git.openjdk.org/jdk/pull/16115