Compact some of the name definitions for wasm opcodes. With the
proposal being in phase 4, the instruction set is fixed, we can now
merge some of the adhoc i64x2 instructions in with the rest.

Bug: v8:11384
Change-Id: I94553b9f2daaa4804deaf1bb18933847897a4213
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2708759Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72988}