RFR: 8331168: Introduce PredicateEntryIterator to iterate through predicate entries

[Christian Hagedorn]

This is another small PR split off from the complete fix for Assertion Predicates.

Changes include:
- Replace predicate matching/skipping code in `build_loop_late_post_work()` to use dedicated walker (i.e. new `PredicateEntryIterator` class) which uses predicate classes.
- New predicate helper classes to improve readability.
- Simple typos and code style updates

Thanks,
Christian

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Commit messages:
 - 8331168: Introduce PredicateEntryIterator to iterate through predicate entries

Changes: https://git.openjdk.org/jdk/pull/19716/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19716&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331168
  Stats: 122 lines in 3 files changed: 80 ins; 22 del; 20 mod
  Patch: https://git.openjdk.org/jdk/pull/19716.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19716/head:pull/19716

PR: https://git.openjdk.org/jdk/pull/19716