RFR: 8367657: C2 SuperWord: NormalMapping demo from JVMLS 2025 [v4]

[Emanuel Peter]

> Demo from here:
> https://inside.java/2025/08/16/jvmls-hotspot-auto-vectorization/
> 
> Cleaned up and enhanced with a JTREG and IR test.
> I also added some additional "generated" normal maps from height functions.
> And I display the resulting image side-by-side with the normal map.
> 
> I decided to put it in a new directory `compiler.gallery`, anticipating other compiler tests that are both visually appealing (i.e. can be used for a "gallery") and that we may want to back up with other tests like IR testing.
> 
> There is a **stand-alone** way to run the demo:
> `java test/hotspot/jtreg/compiler/gallery/NormalMapping.java`
> (though it may only run with JDK22+, probably due some amber features)
> 
> Here some snapshots, but **I really recommend pulling the diff and playing with it, it looks much better in motion**:
> <img width="2000" height="991" alt="image" src="https://github.com/user-attachments/assets/a693fac8-ecf0-43f2-914b-25f76c2f425d" />
> <img width="2000" height="997" alt="image" src="https://github.com/user-attachments/assets/c2202e6b-6a90-4f90-a3ca-b73304e25905" />
> <img width="1997" height="992" alt="image" src="https://github.com/user-attachments/assets/0d6da304-6bb9-4b25-9a7b-72019b02d95e" />
> <img width="1992" height="994" alt="image" src="https://github.com/user-attachments/assets/9f5f7426-0678-45af-a3eb-ac092c262d4c" />

Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:

  Apply suggestions from code review
  
  Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27282/files
  - new: https://git.openjdk.org/jdk/pull/27282/files/47aa0c7d..00416267

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27282&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27282&range=02-03

  Stats: 19 lines in 2 files changed: 0 ins; 3 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/27282.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27282/head:pull/27282

PR: https://git.openjdk.org/jdk/pull/27282