Prototype these 4 instructions:

- i64x2.widen_low_i32x4_s
- i64x2.widen_high_i32x4_s
- i64x2.widen_low_i32x4_u
- i64x2.widen_high_i32x4_u

Implementation is the same as x64.

Drive-by fix to add a missing CpuFeatureScope to x64.

Bug: v8:10972
Change-Id: Iacc84bce156053d0ac39b1a419727c93c499a8c9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2612339
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72025}