Move them all into wasm-macro-gen.h, other opcodes have their macros
there as well. This will make reusing these macros easier when we have
other test files for SIMD. (An upcoming one is for scalar lowering
tests.)

Change-Id: I6c21100ce490abbc26f80a0d204815687fd62f00
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2185471Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67658}