RFR: 8356575: Test order in which jpackage fills app image

[Alexey Semenyuk]

- Test order in which jpackage fills app image
- Fix an issue with jpackage that it would fail to overwrite existing files in the app image. Uncovered by the test.

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Commit messages:
 - 8356575: Test order in which jpackage fills app image

Changes: https://git.openjdk.org/jdk/pull/27826/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27826&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356575
  Stats: 351 lines in 2 files changed: 350 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27826.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27826/head:pull/27826

PR: https://git.openjdk.org/jdk/pull/27826