RFR: 8344587: Reduce number of "jdk.jpackage.internal" classes used from other packages

[Alexey Semenyuk]

Stop using internal AppImageFile, ApplicationLayout, and PackageFile classes in the tests. Replace them with stubs.

Stop referencing IOUtils class from XmlUtils and PathUtils classes.

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Commit messages:
 - Minor improvements
 - Make IOUtils class package-private
 - Bugfix & cleanup
 - Merge branch 'master' into SplitIOUtils.DecoupleAppImageFile
 - Bad merge fix
 - Bad merge fix
 - Make AppImageFile and PackageFile classes package-private
 - Revert "Get rid of FunctionalUtils.java". Brings back Functional.java to make the diff easier to digest. It will be replaced with redoing c58b6587b3b4fb9c08afd27eacf139e0ed9afb83 commit in the next PR.
 - Fix bad merge
 - 8344550: Compilation error of jpackage test JPackageStringBundle.java source
 - ... and 14 more: https://git.openjdk.org/jdk/compare/78602be1...9d1f097d

Changes: https://git.openjdk.org/jdk/pull/22261/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22261&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344587
  Stats: 381 lines in 21 files changed: 288 ins; 61 del; 32 mod
  Patch: https://git.openjdk.org/jdk/pull/22261.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22261/head:pull/22261

PR: https://git.openjdk.org/jdk/pull/22261