RFR: 8367902: Allocation after Universe::before_exit() in the VM shutdown sequence

[Leonid Mesnik]

Please review following fix that move GC shutdown start after VM Death and agent's unloading.

The `Universe::before_exit();` switch GC to fail any new GC allocation. So any allocation in vm death is failing.

The test is a little bit complicated because jtreg uses wrapper even to execute othrevm tests and also results might be confusing if test is failing after main() method is completed. So the better is to run new process for vm death event handling.

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Commit messages:
 - 8367902: Allocation after Universe::before_exit() in the VM shutdown sequence

Changes: https://git.openjdk.org/jdk/pull/28227/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28227&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367902
  Stats: 148 lines in 3 files changed: 145 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28227.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28227/head:pull/28227

PR: https://git.openjdk.org/jdk/pull/28227