RFR: 8305638: Refactor Template Assertion Predicate Bool creation and Predicate code in Split If and Loop Unswitching [v2]

[Christian Hagedorn]

> This patch is intended for JDK 23.
> 
> While preparing the patch for the full fix for Assertion Predicates [JDK-8288981](https://bugs.openjdk.org/browse/JDK-8288981), I still noticed that some changes are not required for the actual fix and could be split off and reviewed separately in this PR.
> 
> The patch applies the following cleanup changes:
> - The complete fix had to add slightly different cloning cases in `PhaseIdealLoop::create_bool_from_template_assertion_predicate()` which already has quite some logic to switch between different cases. Additionally, the algorithm in the method itself was already hard to understand and difficult to adapt. I therefore re-implemented it in a separate class `CloneTemplateAssertionPredicateBool` together with some helper classes like `DFSNodeStack`. To use it, I've added a `TemplateAssertionPredicateBool` class that offers three cloning possibilities:
>   - `clone()`: Clone without modification
>   -  `clone_and_replace_opaque_loop_nodes()`: Clone and replace the `OpaqueLoop*Nodes` with a new init and stride node.
>   - `clone_and_replace_init()`: Special case of `clone_and_replace_opaque_loop_nodes()` which only replaces `OpaqueLoopInitNode` and clones `OpaqueLoopStrideNode`.
>   
>   This refactoring could be extracted from the complete fix.
> - The Split If code to detect (`subgraph_has_opaque()`) and clone Template Assertion Predicate Bools was extracted to a separate class `CloneTemplateAssertionPredicateBoolDown` and uses the new `TemplateAssertionPredicateBool` class to do the actual cloning.
> - In the process of coding the complete fix, I've refactored the Loop Unswitching code quite a bit. This change could also be extracted into a separate RFE. Changes include:
>   - Renaming
>   - Extracting code to separate classes/methods
>   - Adding comments
> - Some small refactoring including:
>   - Removing unused parameters
>   - Renaming variables/parameters/methods
> 
> Thanks,
> Christian

Christian Hagedorn has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - Merge branch 'master' into JDK-8305638
   
   # Conflicts:
   #	src/hotspot/share/opto/loopPredicate.cpp
   #	src/hotspot/share/opto/loopUnswitch.cpp
   #	src/hotspot/share/opto/split_if.cpp
 - Misc renamings/refactoring
 - Refactor Loop Unswitching
 - Refactor Template Assertion Predicate Bool creation and Split If

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Changes: https://git.openjdk.org/jdk/pull/16877/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16877&range=01
  Stats: 927 lines in 11 files changed: 611 ins; 175 del; 141 mod
  Patch: https://git.openjdk.org/jdk/pull/16877.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16877/head:pull/16877

PR: https://git.openjdk.org/jdk/pull/16877