RFR: 8276400: openjdk image Jars, Zips and Jmods built from the same source are not reproducible

[Andrew Leonard]

This PR enables reproducible Jars, Jmods and openjdk image zip files (eg.src.zip).
It provides support for SOURCE_DATE_EPOCH for Jar, Jmod and underlying ZipOutputStream's.
It fixes the following keys issues relating to reproducibility:
- Jar and ZipOutputStream are not SOURCE_DATE_EPOCH aware
  - Jar and ZipOutputStream now detect SOURCE_DATE_EPOCH environment setting
- Jar and Jmod file content ordering was non-determinsitic
  - Fixes to Jar and Jmod main's to ensure sorted classes content ordering
- openjdk image zip file generation used "zip" which is non-determinsitic
  - New openjdk build tool "GenerateZip" which produces the final determinsitic zip files as part of the build and also detects SOURCE_DATE_EPOCH

Signed-off-by: Andrew Leonard <anleonar at redhat.com>

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Commit messages:
 - 8276400: openjdk image Jars, Zips and Jmods built from the same source are not reproducible

Changes: https://git.openjdk.java.net/jdk/pull/6268/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6268&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276400
  Stats: 818 lines in 11 files changed: 797 ins; 3 del; 18 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6268.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6268/head:pull/6268

PR: https://git.openjdk.java.net/jdk/pull/6268