RFR: 8366948: AOT cache creation crashes when iterating training data

[Igor Veresov]

I forgot a lock around `CTD::_ci_records`. It also has to respect the snapshotting protocol. Testing is good.

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Commit messages:
 - Need a lock around _ci_records access. Respect snapshot flag.

Changes: https://git.openjdk.org/jdk/pull/27461/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27461&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366948
  Stats: 6 lines in 1 file changed: 4 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/27461.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27461/head:pull/27461

PR: https://git.openjdk.org/jdk/pull/27461