RFR: 8370123: Minor jpackage refactoring

[Alexey Semenyuk]

On Fri, 17 Oct 2025 18:06:46 GMT, Alexey Semenyuk <asemenyuk at openjdk.org> wrote:

> Minor changes, no functional impact.
> 
> - Move warning logging from MacBaseInstallerBundler to MacPackageBuilder, MacPkgPackageBuilder
> - ApplicationBuilder: add externalApplication() and mainLauncherClassName() methods
> - `AppImageSigner.normalizeAppImageLayout()` -> `AppImageSigner.copyWithUnresolvedAppImageLayout()`
> - Add `JLinkRuntimeBuilder.ensureBaseModuleInModulePath()`; move code away from StandardBundlerParam; remove redundant "warning.no.jdk.modules.found" string ID
> - Add `OverridableResource.probe()` method
> - Remove dead and "odd" code from IOUtils

@sashamatveev PTAL

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PR Comment: https://git.openjdk.org/jdk/pull/27873#issuecomment-3417438642