RFR: 8343220: Add test cases to AppContentTest jpackage test

[Alexey Semenyuk]

On Thu, 23 Oct 2025 05:38:45 GMT, Alexey Semenyuk <asemenyuk at openjdk.org> wrote:

> - Update AppContentTest by adding new test cases as requested in the CR.
> - Fix uncovered issue in jpackage: if the same path in the app image is sourced from a file and a directory values of `--app-content` option, it bails out trying to replace the file with the directory and vice versa.

@sashamatveev PTAL

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PR Comment: https://git.openjdk.org/jdk/pull/27948#issuecomment-3436470486