This is a reland of 660d8287

Original change's description:
> [debug] Mark toLocaleString and TA#join builtins as side-effect free.
>
> Bug: chromium:940373
> Change-Id: If5f90ff5f873f0687c6a6a4063e0d09d6bbbd556
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1533157
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Commit-Queue: Peter Wong <peter.wm.wong@gmail.com>
> Cr-Commit-Position: refs/heads/master@{#60440}

Bug: chromium:940373
Change-Id: I03fe4c06cad9848db211739170462d52ce3f7acf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1538791Reviewed-by: Simon Zünd <szuend@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Peter Wong <peter.wm.wong@gmail.com>
Cr-Commit-Position: refs/heads/master@{#60575}