RFR: 8365555: Cleanup redundancies in jpackage implementation [v3]

[Alexander Matveev]

On Fri, 15 Aug 2025 15:11:09 GMT, Alexey Semenyuk <asemenyuk at openjdk.org> wrote:

>> - Remove AppImageDesc class. It was supposed to bind an AppImageLayout instance with a root directory, but since AppImageLayout has `rootDirectory()` method it is redundant.
>>  - Remove redundant `Package.packageLayout()` and `Package.asPackageApplicationLayout()` methods from the model, 
>>  - Add tests for PackagingPipeline class.
>>  - Move JUnitAdapter.java from "/test/jdk/tools/jpackage/helpers-test" to "/test/jdk/tools/jpackage/junit/tools" directory, support running platform-specific JUnit tests.
>>  - Enhance AppImageLayout class, add unit tests for derived MacApplicationLayout and LinuxApplicationLayout classes.
>>  - Add tests for BuildEnv class.
>
> Alexey Semenyuk has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix issues uncovered when running signing tests

Looks good.

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Marked as reviewed by almatvee (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26778#pullrequestreview-3125174254