We are running out of encoding space for opcodes on arm64. This patch
merges some wasm simd opcodes of different simd types, encoding the lane
size in the instruction code using LaneSizeField instead. This reduces
the total number of opcodes on arm64 by 71.

Bug: v8:12093
Change-Id: Ib4d96d1db1ff9b08fafd665974f3494a507da770
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3109676Reviewed-by: Zhi An Ng <zhin@chromium.org>
Commit-Queue: Martyn Capewell <martyn.capewell@arm.com>
Cr-Commit-Position: refs/heads/main@{#76434}