[llvm] [WebAssembly] Fold constant `i8x16.swizzle` and `i8x16.relaxed.swizzle` to `shufflevector` (PR #169110)

[Derek Schuff via llvm-commits]

dschuff wrote:

> Not sure what our position on Claude, though in this case it is just for the test.

General LLVM [position](https://llvm.org/docs/DeveloperPolicy.html#ai-generated-contributions) is that it's fine, but that contributors are responsible for their contributions just as if they wrote it themselves. I think this PR is getting plenty of review so I'm not worried.

https://github.com/llvm/llvm-project/pull/169110