RFR: 8356575: Test order in which jpackage fills app image [v3]

[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.

Alexey Semenyuk has updated the pull request incrementally with one additional commit since the last revision:

  Use Files.mismatch() to check if the content of two files mismatch or not. Add TKit.assertMismatchFileContent() and TKit.assertSameFileContent() helper functions.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27826/files
  - new: https://git.openjdk.org/jdk/pull/27826/files/15c5d6fa..0db2749f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27826&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27826&range=01-02

  Stats: 63 lines in 3 files changed: 35 ins; 24 del; 4 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