All jpackage jtreg test declarations have @modules tag. Values:
  jdk.jpackage/jdk.jpackage.internal
AppContentTest.java additionally has "@modules java.base/jdk.internal.util" tag

All jpackage jtreg test declarations have @library tag. Values:
  ../../../../helpers
  ../helpers
This @library tag is properly accompanied by the "@build jdk.jpackage.test.*" tag, which pulls in all classes from the jpackage test helper library.

Other @library tag values:
  /test/lib
  base
These are probably dangling ends because they are not accompanied by relevant @build tags.

Some @run tags have "--add-opens jdk.jpackage/jdk.jpackage.internal=ALL-UNNAMED". These tests pull in jpackage helper lib functionality that uses reflection to access jpackage internal classes. E.g.: https://github.com/openjdk/jdk/blob/1b177ce5b7e25b3a563066ba92dbf8cacfd29126/test/jdk/tools/jpackage/helpers/jdk/jpackage/test/LauncherIconVerifier.java#L161

This `--add-opens` should be applied to jpackage test lib.

jpackage jtreg test declarations should be unified:
 - remove "@modules java.base/jdk.internal.util"
 - remove `--add-opens` from @run
 - replace "@library ../../../../helpers" and "@library ../helpers" with "@library /test/jdk/tools/jpackage/helpers"
 - remove @library referring unused libraries.

Add "modules=jdk.jpackage/jdk.jpackage.internal:+open java.base/jdk.internal.util" to jpackage's TEST.properties. This will eliminate the need for `--add-open` and "@modules java.base/jdk.internal.util" in jtreg test declarations. This change will simplify jpackage jtreg test declarations, reduce code duplication, and do a cleanup.