RFR: 8370156: Fix jpackage IconTest [v3]

[Alexey Semenyuk]

On Wed, 22 Oct 2025 04:27:43 GMT, Alexey Semenyuk <asemenyuk at openjdk.org> wrote:

>> Rework IconTest.
>> 
>> Verified it produces the output as expected.
>> 
>> It still will not catch [JDK-8370155](https://bugs.openjdk.org/browse/JDK-8370155). However, this is deliberate to avoid significant changes in the test and implementation in a single commit.
>
> Alexey Semenyuk has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:
> 
>  - Rollback JDK-8370100 specific patch
>  - IconTest: revamp

@sashamatveev PTAL

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PR Comment: https://git.openjdk.org/jdk/pull/27883#issuecomment-3432205731