[jdk17] RFR: 8271155: Wrong path separator in env variable

[Alexey Semenyuk]

Replace `";"` with `FileUtils::pathSeparator` in the expression adding 'app' dir to env variable in jpackage app launcher.

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Commit messages:
 - 8271155: Wrong path separator in env variable

Changes: https://git.openjdk.java.net/jdk17/pull/271/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17&pr=271&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271155
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk17/pull/271.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17 pull/271/head:pull/271

PR: https://git.openjdk.java.net/jdk17/pull/271