RFR: 8320858: Move jpackage tests to tier3

[Alan Bateman]

Update the jtreg test group configuration in the jdk test tree so that the jpackage tests run in tier3 rather than tier2.

At this time, the jpackage tests run in jdk:tier2, more specifically jdk:tier2_part2 as part of the core_tools test group. The  jpackage tests take a significant amount of time on some platforms (on macOS and Windows in particular). The changes here remove tools/jpackage from core_tools (it's not a core tool anyway) and adds the tests to tier3. In the future then maybe tier3 can be split up if needed.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/16841/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16841&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320858
  Stats: 11 lines in 1 file changed: 6 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/16841.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16841/head:pull/16841

PR: https://git.openjdk.org/jdk/pull/16841