[lworld] RFR: 8371429: [lworld] Fix package name inference for ResourcePoolManager for preview mode

[David Beaumont]

Switches package inference to handle preview resource paths.

Additionally:
* Updates unit test to use JUnit.
* Deletes unused code (both newly unused and previously unused).

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Commit messages:
 - Fix resource pool package name inference.

Changes: https://git.openjdk.org/valhalla/pull/1724/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1724&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371429
  Stats: 288 lines in 3 files changed: 94 ins; 147 del; 47 mod
  Patch: https://git.openjdk.org/valhalla/pull/1724.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1724/head:pull/1724

PR: https://git.openjdk.org/valhalla/pull/1724