This reimplements the "--time" option of run-tests.py to print the
20 slowest tests, on top of json_test_results infrastructure just
like the bots do it.
Additionally this CL speeds up a bunch of slow tests.

Bug: v8:9396
Change-Id: I40797d2c8c3bfdd310b72f15cd1a035844b7c6f3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1803635
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63786}