[WebAssembly] Add tests ensuring rotates persist

Due to the nature of WebAssembly, it's always better to keep
rotates instead of trying to optimize it. Commit 9485d983
disabled the generation of fsh for rotates, however these
tests ensure that future changes don't change the behaviour for
the Wasm backend that tends to have different optimization
requirements than other architectures. Also see:
https://github.com/llvm/llvm-project/issues/62703

Differential Revision: https://reviews.llvm.org/D152126