RFR: 8372451: C2 SuperWord: "endless loop" assert. Need to implement proper worklist mechanism [v3]

[Emanuel Peter]

> **Context**: `VTransform::optimize`. Works a bit like IGVN, it allows each node to perform optimizations. Recently introduced during JDK26.
> 
> **Problem**: I made the assumption that we don't need a worklist mechanism, we can just do multiple passes over all nodes. The assumption was that there would not be any "trickling" of updates over the graph. But that is wrong: for example we can have a long chain of dead nodes, and we need to progressively remove the last node and mark it as dead.
> 
> **Solution**: Implement proper worklist mechanism, so that updates can trickle over the graph.

Emanuel Peter 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 11 additional commits since the last revision:

 - Merge branch 'master' into JDK-8372451-too-many-dead-vector-reduction-vtnodes
 - Apply suggestions from code review
   
   Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
 - limit steps of optimize, for Manuel
 - Merge branch 'master' into JDK-8372451-too-many-dead-vector-reduction-vtnodes
 - rm old documentation
 - git move to new test
 - streamline
 - refactor and verify
 - unique worklist
 - wip solution
 - ... and 1 more: https://git.openjdk.org/jdk/compare/a4a5fdb0...54881ff4

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28512/files
  - new: https://git.openjdk.org/jdk/pull/28512/files/9f5bf837..54881ff4

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28512&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28512&range=01-02

  Stats: 12411 lines in 291 files changed: 6379 ins; 5081 del; 951 mod
  Patch: https://git.openjdk.org/jdk/pull/28512.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28512/head:pull/28512

PR: https://git.openjdk.org/jdk/pull/28512