[WebAssembly] Finalize SIMD names and opcodes

Updates the names (e.g. widen => extend, saturate => sat) and opcodes of all
SIMD instructions to match the finalized SIMD spec. Deliberately does not change
the public interface in wasm_simd128.h yet; that will require more care.

Depends on D98466.

Differential Revision: https://reviews.llvm.org/D98676