[WebAssembly] Fix types in wasm_simd128.h and add tests

47f7174f changed the types used in the Wasm SIMD builtin functions,
but not all of their uses in wasm_simd128.h were updated. This commit
fixes wasm_simd128.h and adds tests to make sure similar problems do
not pass uncaught in the future.

Differential Revision: https://reviews.llvm.org/D85347