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

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

Is it possible to do this as a DAG combine and avoid adding a new pass

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