Stop using internal AppImageFile, ApplicationLayout, and PackageFile classes in the tests. Replace them with stubs.
It was handy to use them, but from now on, it is better to decouple jpackage internals from the tests.

Stop referencing IOUtils class from XmlUtils and PathUtils classes.

Make IOUtils, AppImageFile, ApplicationLayout, and PackageFile classes package-private to prevent accidental use from outside "jdk.jpackage.internal" package.