This adds two flags for whitelisting natives on fuzzers:
--allow-natives-for-fuzzing:
Enables a small subset of runtime functions and replaces others with
undefined.
--allow-natives-for-differential-fuzzing
Restricts the allowed runtime functions even further, excluding the
ones that break differential fuzzing.

Bug: chromium:1044942
Change-Id: I890bd4a6ff7c2e483dd74155290a7ace06f85239
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2020773Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66068}