jpackager has it's own simplistic implementation of @argfile.
In order to have the same implementation of this code is in javac, we should just take a copy of src/jdk.compiler/share/classes/com/sun/tools/javac/main/CommandLine.java, change only the package name, and include it in jpackage.
If at some future point this migrates to a public API or even an internal jdk module, we can just call it. In the meantime we can maintain this copy.