This relands commit 7d955faa.

Changed the test case to use i16x8 splat instead of i8x16 splat,
the latter was causing issues when doing scalar lowering. This
change still causes the regression test to fail without the fix.

Original change's description:
> [wasm-simd][x64][ia32] Do not overwrite input register
>
> We are ovewriting input register (contains the shift) when we are
> masking it, instead, move to a temporary,then mask it.
>
> Bug: chromium:1065599
> Change-Id: Iab72b94581239447e444746681387350b576e24a
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2125941
> Commit-Queue: Zhi An Ng <zhin@chromium.org>
> Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#66997}

Bug: chromium:1065599
Change-Id: I0dc78ddb013652ef88c07d065c3f6877937c5300
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2136220Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67026}