Reland "[regexp] Enable fallback to experimental engine by default"

This reverts commit 9417dae4.

Bug: v8:10765,v8:11021
Change-Id: I138d794cc3339ed58a343f8150730af5a1f3e511
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2485791Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Martin Bidlingmaier <mbid@google.com>
Cr-Commit-Position: refs/heads/master@{#70644}

src/flags/flag-definitions.h

@@ -1500,7 +1500,7 @@ DEFINE_BOOL(enable_experimental_regexp_engine, false,
 DEFINE_BOOL(trace_experimental_regexp_engine, false,
             "trace execution of experimental regexp engine")
 
-DEFINE_BOOL(enable_experimental_regexp_engine_on_excessive_backtracks, false,
+DEFINE_BOOL(enable_experimental_regexp_engine_on_excessive_backtracks, true,
             "fall back to a breadth-first regexp engine on excessive "
             "backtracking")
 DEFINE_UINT(regexp_backtracks_before_fallback, 10000,