RFR: 8361144: Strenghten the Ideal Verification in PhaseIterGVN::verify_Ideal_for by comparing the hash of a node before and after Ideal [v4]

[Benoît Maillard]

> This PR adds a node hash comparison after calling `Ideal` in `PhaseIterGVN::verify_Ideal_for` to introduce an additional layer of verification for missed optimizations. Previously, we relied on the return value of `Ideal`, which is expected to be `nullptr` if no transformation was done.
> 
> By also checking the node's hash before and after `Ideal`, we could catch inconsistencies in the implementation or unintended modifications to the graph. Both of these may indicate missed or incomplete optimizations.
> 
> ### Testing
> - [x] [GitHub Actions](https://github.com/benoitmaillard/jdk/actions?query=branch%3AJDK-8361144)
> - [x] tier1-3, plus some internal testing
> 
> Thank you for reviewing!

Benoît Maillard 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 six additional commits since the last revision:

 - Merge branch 'master' into JDK-8361144
 - 8361144: add comment for consistency with node count
 - 8361144: update comment
   
   Co-authored-by: Damon Fenacci <damon.fenacci at oracle.com>
 - 8361144: remove unintentional line break
 - 8361144: move hash check after return value check and use same format as unique counter check
 - 8361144: add check for node hash after verifying ideal

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26064/files
  - new: https://git.openjdk.org/jdk/pull/26064/files/75f81296..8660d6ae

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26064&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26064&range=02-03

  Stats: 18711 lines in 635 files changed: 10936 ins; 3423 del; 4352 mod
  Patch: https://git.openjdk.org/jdk/pull/26064.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26064/head:pull/26064

PR: https://git.openjdk.org/jdk/pull/26064