Fuzz non-v8-supported features more (#8448)

We have seen some continuation-related bugs recently, that more
fuzzing could have found. Fuzz v8 a little less to add coverage there.

Author: kripken

scripts/fuzz_opt.py

@@ -147,11 +147,11 @@ def randomize_feature_opts():
                 FEATURE_OPTS.append(possible)
                 if possible in IMPLIED_FEATURE_OPTS:
                     FEATURE_OPTS.extend(IMPLIED_FEATURE_OPTS[possible])
-    elif random.random() < 0.9:
-        # 90% of the remaining (2/3 * 0.9) use them all (0.54 probability). This is useful to maximize
-        # coverage, as enabling more features enables more optimizations and
-        # code paths, and also allows all initial contents to run.
-
+    # Otherwise, use all the features. This is useful to maximize
+    # coverage, as enabling more features enables more optimizations and
+    # code paths, and also allows all initial contents to run. However,
+    # half the time disable the specific ones that are a problem in V8.
+    elif random.random() < 0.5:
         # Disable features not allowed in V8 to increase V8 fuzzing.
         FEATURE_OPTS.extend(f'--disable-{feature}' for feature in DISALLOWED_FEATURES_IN_V8)
         # Relaxed SIMD's nondeterminism disables much but not