RFR: 8317678: Fix up hashCode() for ZipFile.Source.Key [v3]

[Sean Coffey]

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

Sean Coffey has updated the pull request incrementally with one additional commit since the last revision:

  insert back lastmodified check. enhance testcase. more review comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16115/files
  - new: https://git.openjdk.org/jdk/pull/16115/files/847d0bd1..f930fac9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16115&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16115&range=01-02

  Stats: 98 lines in 2 files changed: 53 ins; 16 del; 29 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