RFR: 8375272: [IR Framework] Miscellaneous clean-ups

[Christian Hagedorn]

This patch applies various unrelated clean-ups split out from a first prototype for [JDK-8375270](https://bugs.openjdk.org/browse/JDK-8375270). This should ease reviews. I left some comments in the PR to further explain some details.

Thanks,
Christian

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Commit messages:
 - fix tests
 - fix tests
 - fix build
 - cleanups

Changes: https://git.openjdk.org/jdk/pull/29362/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29362&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375272
  Stats: 162 lines in 15 files changed: 81 ins; 12 del; 69 mod
  Patch: https://git.openjdk.org/jdk/pull/29362.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29362/head:pull/29362

PR: https://git.openjdk.org/jdk/pull/29362