[jdk21u-dev] RFR: 8317678: Fix up hashCode() for ZipFile.Source.Key

[Satyen Subramaniam]

Backporting JDK-8317678: Fix up hashCode() for ZipFile.Source.Key. Fixes java.util.zip.ZipFile$Source hashCode() impl so that duplicate Source objects aren't created for the same zip file. Adds test. Ran GHA Sanity Checks, local Tier 1 and 2, and new test. Patch is clean.

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Commit messages:
 - Backport 8d9a4b43f4fff30fd217dab2c224e641cb913c18

Changes: https://git.openjdk.org/jdk21u-dev/pull/1729/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1729&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317678
  Stats: 189 lines in 3 files changed: 188 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1729.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1729/head:pull/1729

PR: https://git.openjdk.org/jdk21u-dev/pull/1729