We fall back from irregexp to the experimental engine if a backtrack
limit is exceeded and the experimental engine can handle the regexp.
The feature can be turned on with a boolean flag, and an uint-valued
flag controls the default backtrack limit.  For regexps that are
constructed with an explicit backtrack limit (API,
%NewRegExpWithBacktrackLimit), we choose the lower of the explicit and
default backtrack limits.
The default backtrack limit does not apply to regexps that can't be
handled by the experimental engine, and for such regexps an explicitly
specified backtrack limit is handled as before by returning null if we
exceed it.

Cq-Include-Trybots: luci.v8.try:v8_linux64_fyi_rel_ng
Bug: v8:10765
Change-Id: I580df79bd847520985b6c2c2159bc427315c89d1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2436341
Commit-Queue: Martin Bidlingmaier <mbid@google.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70500}