RFR: 8356575: Test order in which jpackage fills app image [v2]

[Alexey Semenyuk]

On Wed, 15 Oct 2025 18:24:02 GMT, Alexey Semenyuk <asemenyuk at openjdk.org> wrote:

>> - 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:
> 
>   Refactor. Simplify and make it pass on Windows and Linux

Use `Files.mismatch()` instead of comparing file digests in the test.

@sashamatveev, please review again

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PR Comment: https://git.openjdk.org/jdk/pull/27826#issuecomment-3416381506