[wasm][revec] Mark revectorization as experimental

R=clemensb@chromium.org

Bug: chromium:1463850
Change-Id: I66a9e9f5f3eea2455f69b60b3a909d6affb0c880
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4689698
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#89027}

src/flags/flag-definitions.h

@@ -1442,8 +1442,9 @@ DEFINE_DEBUG_BOOL(trace_wasm_instances, false,
 
 // Flags for WASM SIMD256 revectorize
 #ifdef V8_ENABLE_WASM_SIMD256_REVEC
-DEFINE_BOOL(experimental_wasm_revectorize, false,
-            "enable 128 to 256 bit revectorization for Webassembly SIMD")
+DEFINE_EXPERIMENTAL_FEATURE(
+    experimental_wasm_revectorize,
+    "enable 128 to 256 bit revectorization for Webassembly SIMD")
 DEFINE_BOOL(trace_wasm_revectorize, false, "trace wasm revectorize")
 #endif  // V8_ENABLE_WASM_SIMD256_REVEC