1. Child classes of jdk.jpackage.test.Functional class [1] in the jpackage test lib can be used in the jpackage implementation. They are handy to deal with checked exceptions in lambda expressions. Move these classes to the new "jdk.jpackage.internal.util.function" package.

2. jpackage IOUtils class [2] is a pile of utility functions used by both jpackage implementation and jpackage test lib. Move its contents between XmlUtils, PathUtils, FileUtils classes. Functions that fit in none of these classes should remain in the IOUtils class. Add new classes in "jdk.jpackage.internal.util" package.

Introducing new "jdk.jpackage.internal.util.function" and "jdk.jpackage.internal.util" packages will add a structure to jpackage sources.

[1] https://github.com/openjdk/jdk/blob/dfddbcaab886b9baa731cd748bb7f547e1903b64/test/jdk/tools/jpackage/helpers/jdk/jpackage/test/Functional.java
[2] https://github.com/openjdk/jdk/blob/dfddbcaab886b9baa731cd748bb7f547e1903b64/src/jdk.jpackage/share/classes/jdk/jpackage/internal/IOUtils.java