The extra checks done with --testing-d8-test-runner might not hold
when using NumFuzz. This refactors the test runner and allows passing
implementation specific flags. The --testing-d8-test-runner flag is
now only passed in the standard-runner not in the numfuzz
implementation.

Bug: v8:10220
Change-Id: I83cac57a948c98c34f2d84f41d719e0434e25ee7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2064217
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66341}