In this part: splice, flat, flatMap

Bug: v8:11111
Change-Id: Ide06c1137c6b4def70d09d479cfbedfb2d7c8450
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3755106Reviewed-by: Shu-yu Guo <syg@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81657}