RFR: 8358580: Rethink how classes are kept alive in training data

[Igor Veresov]

Use OopStorage directly instead of JNI handles. Note that we never destroy TrainingData objects, so we don't need to concern ourselves with freeing the OopStorage entries. Also, keeping the klasses alive is only necessary during the training run. During the replay the klasses TD objects refer to are always alive.

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Commit messages:
 - Use OopStorage directly instead on JNI handles

Changes: https://git.openjdk.org/jdk/pull/26233/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26233&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358580
  Stats: 12 lines in 2 files changed: 6 ins; 2 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/26233.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26233/head:pull/26233

PR: https://git.openjdk.org/jdk/pull/26233