RFR: 8359174: tools/jlink/JLink20000Packages.java timed out

[Henry Jen]

Create a jar directly from the memory instead of real file, this should reduce the I/O overhead which likely the reason for the time out.
The issue is not reproducible locally, and fails intermittently, so we simply trying to reduce time needed.
The jar file created is verified manually running jtreg with retain=all.

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Commit messages:
 - cleanup
 - 8359174: tools/jlink/JLink20000Packages.java timed out

Changes: https://git.openjdk.org/jdk/pull/25981/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25981&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8359174
  Stats: 30 lines in 2 files changed: 6 ins; 12 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/25981.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25981/head:pull/25981

PR: https://git.openjdk.org/jdk/pull/25981