WASM only supports simd128, but modern CPUs support
up to 256 bit vector register or more, we will add an
experimental feature to do 256 bit re-vectorization
in Turbofan pipeline, this patch add simd256 machine
representation.

Bug: v8:12716
Change-Id: I1e6a3f2afa0a457fca2c261216f4113d0ed5b818
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3534456Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Jie Pan <jie.pan@intel.com>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80361}