This is a reland of 21e47944

The fix is in the encoding of vmov. Bit 23 (the U bit) should be 0,
whether the NeonDataType is NeonS32 or NeonU32. Also added a DCHECK
in the simulator to assert this.

Original change's description:
> [wasm-simd][arm] Prototype i64x2.bitmask
>
> Cleanup to simulator to remove repetitive logic to get instruction
> fields.
>
> Bug: v8:10997
> Change-Id: I01f0b99f85788b41e4cab505fc94362d637c396f
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2554256
> Commit-Queue: Zhi An Ng <zhin@chromium.org>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Reviewed-by: Bill Budge <bbudge@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#71391}

Bug: v8:10997
Change-Id: I93b5d2168a50446d4a3b487ad83d6af8ea9ba8ab
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2558262
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71467}