This is a reland of 0347f00a

Original change's description:
> Refactor platform tests to avoid deprecated API
>
> The old tasks API is deprecated and we want to remove it in 8.0.
> Thus, this CL refactors the platform tests to use the new
> TaskRunner-based API, and removes redundant tests.
>
> R=ahaas@chromium.org
>
> Bug: v8:9810
> Change-Id: Ie53c90184639e77b3247228059fd88290b233e0c
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1868619
> Reviewed-by: Andreas Haas <ahaas@chromium.org>
> Commit-Queue: Clemens Backes <clemensb@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#64412}

Bug: v8:9810
Cq-Include-Trybots: luci.v8.try:v8_linux64_msan_rel
Change-Id: I0f66791828e0f605a67f9af575dbead35e8feb9d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1871917Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64425}