Reland "[rab/gsab] Temporarily stage --harmony-rab-gsab to enable fuzzing"

This reverts commit 24286b8e.

Reason for revert: Re-staging the experimental flag for fuzzing

Original change's description:
> Revert "[rab/gsab] Temporarily stage --harmony-rab-gsab to enable fuzzing"
>
> This reverts commit b8f88be0.
>
> Reason: disabling an experimental feature in release branch
>
> Bug: v8:11111,v8:12870
> Change-Id: I6fbd6bdb318c0d25e69c04db208a0d5f2b9ebbd7
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3647357
> Auto-Submit: Marja Hölttä <marja@chromium.org>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#80520}

Bug: v8:11111,v8:12870
Change-Id: I0a45ed5ce53010196949dda23773d152aa605846
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3647836
Commit-Queue: Marja Hölttä <marja@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#80576}

src/flags/flag-definitions.h

@@ -299,8 +299,6 @@ DEFINE_BOOL(harmony_shipping, true, "enable all shipped harmony features")
   V(harmony_weak_refs_with_cleanup_some,                                       \
     "harmony weak references with FinalizationRegistry.prototype.cleanupSome") \
   V(harmony_import_assertions, "harmony import assertions")                    \
-  V(harmony_rab_gsab,                                                          \
-    "harmony ResizableArrayBuffer / GrowableSharedArrayBuffer")                \
   V(harmony_temporal, "Temporal")                                              \
   V(harmony_shadow_realm, "harmony ShadowRealm")                               \
   V(harmony_struct, "harmony structs and shared structs")
@@ -315,8 +313,11 @@ DEFINE_BOOL(harmony_shipping, true, "enable all shipped harmony features")
 #endif
 
 // Features that are complete (but still behind the --harmony flag).
-#define HARMONY_STAGED_BASE(V) \
-  V(harmony_array_grouping, "harmony array grouping")
+// --harmony-rab-gsab is staged temporarily to enable fuzzing.
+#define HARMONY_STAGED_BASE(V)                        \
+  V(harmony_array_grouping, "harmony array grouping") \
+  V(harmony_rab_gsab,                                 \
+    "harmony ResizableArrayBuffer / GrowableSharedArrayBuffer")
 
 #ifdef V8_INTL_SUPPORT
 #define HARMONY_STAGED(V) HARMONY_STAGED_BASE(V)