Partial implementation of v128.const, only the optimized case for all 0s
and all 1s. The other cases bailout to TurboFan for now, and will be
added in subsequent patches.

Bug: v8:9909
Change-Id: I3240c1c5f4259c45d51edca00fec37047bc1b3a5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2284212
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68772}