RFR: 8321299: runtime/logging/ClassLoadUnloadTest.java doesn't reliably trigger class unloading [v3]

[Matias Saavedra Silva]

> ClassLoadUnloadTest.java passes by accident because an unrelated LambdaForm is being unloaded. The test class, `test.Empty` should be loaded by a custom class loader and then subsequently unloaded, however this is not actually occurring due to the sub-process not receiving the class path. This patch modifies `ClassUnloadCommon`, so it may accept a string containing the classlist, and `ClassLoadUnloadTest.java` so it checks specifically for `test.Empty` to be unloaded. Verified with tier1-5 tests.

Matias Saavedra Silva has updated the pull request incrementally with two additional commits since the last revision:

 - Reverted ClassUnloadCommon
 - Cleanup

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18207/files
  - new: https://git.openjdk.org/jdk/pull/18207/files/c10369fd..92bca7df

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18207&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18207&range=01-02

  Stats: 5 lines in 2 files changed: 2 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18207.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18207/head:pull/18207

PR: https://git.openjdk.org/jdk/pull/18207