RFR: 8358580: Rethink how classes are kept alive in training data [v2]

[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.

Igor Veresov has updated the pull request incrementally with one additional commit since the last revision:

  Address review comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26233/files
  - new: https://git.openjdk.org/jdk/pull/26233/files/e262230b..80d33dab

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26233&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26233&range=00-01

  Stats: 10 lines in 2 files changed: 0 ins; 6 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