This is a reland of de88bfb2

Original change's description:
> [wasm-simd] Implement remaining I8x16 SIMD ops on x64
> 
>  - Implementation for I8x16 Shifts, and Mul
>  - Fix convert bug
>  - Enable all tests except for shuffle tests
> 
> Change-Id: Id1a469d2883c30ea782c51d21dc462d211f94420
> Reviewed-on: https://chromium-review.googlesource.com/c/1318609
> Reviewed-by: Bill Budge <bbudge@chromium.org>
> Commit-Queue: Deepti Gandluri <gdeepti@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#57254}

Change-Id: Id2f6eef3a07e40df37af29456116754e7cf5b901
Reviewed-on: https://chromium-review.googlesource.com/c/1320031Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Deepti Gandluri <gdeepti@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57326}