[jdk21u-dev] RFR: 8334320: Replace vmTestbase/metaspace/share/TriggerUnloadingWithWhiteBox.java with ClassUnloadCommon from testlibrary

[Goetz Lindenmaier]

I backport this for parity with 21.0.9-oracle.

Resolved copyright as 8345795: Update copyright year to 2024 for hotspot in files where it was missed is not in 21/17.

Probably clean anyways.

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Commit messages:
 - Backport 9b49597244f898400222cfc252f50a2401ca3e2f

Changes: https://git.openjdk.org/jdk21u-dev/pull/1945/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1945&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334320
  Stats: 44 lines in 3 files changed: 0 ins; 38 del; 6 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1945.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1945/head:pull/1945

PR: https://git.openjdk.org/jdk21u-dev/pull/1945