This adds the new JsRegExp::Type EXPERIMENTAL, which should eventually
be implemented with the algorithm based on automata. Currently the new
engine deals with plain search strings only, i.e. regexps that do not
contain operators or escape sequences.

R=jgruber@chromium.org

Bug: v8:10765
Change-Id: I6a10d9cdf4605d219dbe7cc1989df3bfa7349ff8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2339094Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69442}