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

[David Holmes]

On Fri, 17 Jan 2025 13:43:35 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

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

I think it reasonable to reduce direct dependencies on WhiteBox, but I don't see any point in having `TriggerUnloadingWithFullGC` when the user of it can use `triggerUnloading()` directly. This framework may have been used more broadly in the past but today I see only a single implementation of `TriggerUnloadingHelper` so it too seems unnecessary. There is really only one reliable way to trigger class unloading and that is ultimately via WhiteBox.

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Changes requested by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23174#pullrequestreview-2568865846