RFR: 8370123: Minor jpackage refactoring

[Alexey Semenyuk]

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

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Commit messages:
 - JLinkRuntimeBuilder: remove trailing whitespace
 - JLinkRuntimeBuilder: add a comment
 - IOUtils: remove dead code; remove getFileName(), getParent() functions.
 - ApplicationLaunchers: minor
 - OverridableResource: add probe() method
 - Add JLinkRuntimeBuilder.ensureBaseModuleInModulePath()
 - AppImageSigner: better function name
 - ApplicationBuilder: add externalApplication() and mainLauncherClassName() methods
 - MacPackageBuilder, MacPkgPackageBuilder: move warning logging from MacBaseInstallerBundler

Changes: https://git.openjdk.org/jdk/pull/27873/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27873&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8370123
  Stats: 295 lines in 16 files changed: 109 ins; 166 del; 20 mod
  Patch: https://git.openjdk.org/jdk/pull/27873.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27873/head:pull/27873

PR: https://git.openjdk.org/jdk/pull/27873