[WebAssembly] Enable recently implemented SIMD operations

Summary:
Moves a batch of instructions from unimplemented-simd128 to simd128
because they have recently become available in V8.

Reviewers: aheejin

Subscribers: dschuff, sbc100, jgravelle-google, hiraditya, sunfish, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D73926