RFR: 8346929: runtime/ClassUnload/DictionaryDependsTest.java fails with "Test failed: should be unloaded"

[Coleen Phillimore]

Adopt the new ClassUnloadCommon.triggerUnloading API to make the unloading tests more reliable.
Tested with tier1 on all platforms.

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Commit messages:
 - Fix some more triggerUnloading() in tests.
 - 8346929: runtime/ClassUnload/DictionaryDependsTest.java fails with "Test failed: should be unloaded"

Changes: https://git.openjdk.org/jdk/pull/22974/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22974&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346929
  Stats: 79 lines in 11 files changed: 29 ins; 22 del; 28 mod
  Patch: https://git.openjdk.org/jdk/pull/22974.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22974/head:pull/22974

PR: https://git.openjdk.org/jdk/pull/22974