This fuzzer randomly generates calls to regexp builtins, runs each on
the slow and fast path, and verifies that their result is the same.

Change-Id: Ia91b0c8afcdaf64835a9bb7b9a470610fbb75fc8
Reviewed-on: https://chromium-review.googlesource.com/833922
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50670}