RFR: 8288: Clean up warnings [v2]

[Marcus Hirt]

> Cleaning up some of the warnings in core in preparation for hack-commit-push (https://switzerland2024.hack-commit-pu.sh/). The ones related to the security manager being deprecated will be taken care of in JMC 10 (https://bugs.openjdk.org/browse/JMC-8289).

Marcus Hirt has updated the pull request incrementally with one additional commit since the last revision:

  Forgot a copyright

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Changes:
  - all: https://git.openjdk.org/jmc/pull/604/files
  - new: https://git.openjdk.org/jmc/pull/604/files/57110e06..ecbb36be

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jmc&pr=604&range=01
 - incr: https://webrevs.openjdk.org/?repo=jmc&pr=604&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jmc/pull/604.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/604/head:pull/604

PR: https://git.openjdk.org/jmc/pull/604