[wasm] Enable --experimental-liftoff-extern-ref by default

R=thibaudm@chromium.org

Bug: v8:7581
Change-Id: I717466f045473015c8d99d1e640492486d05a832
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2625886
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72121}

src/flags/flag-definitions.h

@@ -822,7 +822,7 @@ DEFINE_BOOL(liftoff_only, false,
 DEFINE_IMPLICATION(liftoff_only, liftoff)
 DEFINE_NEG_IMPLICATION(liftoff_only, wasm_tier_up)
 DEFINE_NEG_IMPLICATION(fuzzing, liftoff_only)
-DEFINE_BOOL(experimental_liftoff_extern_ref, false,
+DEFINE_BOOL(experimental_liftoff_extern_ref, true,
             "enable support for externref in Liftoff")
 DEFINE_DEBUG_BOOL(
     enable_testing_opcode_in_wasm, false,