RFR: 8346774: Use Predicate classes instead of Node classes [v2]

[Christian Hagedorn]

> This small cleanup PR replaces a lot of usages of `Node` pointers, to pass around either the head (i.e. `IfNode`) or the tail (i.e. a success projection) of predicates, with actual `Predicate` classes. This simplifies the usages, readability and the logical flow, and enables more simplifications in the future, especially once we replace Template Assertion Predicates with a dedicated node.
> 
> I've also included some minor refactorings like adding `const` or fixing typos.
> 
> There are no semantic changes involved. The return value optimization should take care to avoid a lot of copies when returning new objects from methods. 
> 
> Thanks,
> Christian

Christian Hagedorn has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Review Emanuel
 - Merge branch 'master' into JDK-8346774
 - more cleanups
 - more cleanups
 - 8346774: Use Predicate classes instead of Node classes

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/23234/files
  - new: https://git.openjdk.org/jdk/pull/23234/files/a44280ba..531763da

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23234&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23234&range=00-01

  Stats: 39199 lines in 2918 files changed: 17712 ins; 11939 del; 9548 mod
  Patch: https://git.openjdk.org/jdk/pull/23234.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23234/head:pull/23234

PR: https://git.openjdk.org/jdk/pull/23234