RFR: 8334320: Replace vmTestbase/metaspace/share/TriggerUnloadingWithWhiteBox.java with ClassUnloadCommon from testlibrary

[Coleen Phillimore]

Rename and make TriggerUnloadingWithWhiteBox call ClassUnloadCommon.triggerUnloading() instead of WB.fullGC().

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Commit messages:
 - 8334320: Replace vmTestbase/metaspace/share/TriggerUnloadingWithWhiteBox.java with ClassUnloadCommon from testlibrary

Changes: https://git.openjdk.org/jdk/pull/23174/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23174&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334320
  Stats: 80 lines in 4 files changed: 36 ins; 38 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/23174.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23174/head:pull/23174

PR: https://git.openjdk.org/jdk/pull/23174