[wasm][eh] Fix initial map for W.Exception

Just re-use the error constructor's initial map for the
WebAssembly.Exception constructor, instead of creating a new one.

R=jkummerow@chromium.org

Bug: v8:11992
Change-Id: If1ee53a1e9492c9ab4b59e363b388260ff097cf5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3071211Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76108}

src/wasm/wasm-js.cc

@@ -2638,8 +2638,10 @@ void WasmJs::Install(Isolate* isolate, bool exposed_on_global_object) {
     Handle<JSFunction> exception_constructor = InstallConstructorFunc(
         isolate, webassembly, "Exception", WebAssemblyException);
     SetDummyInstanceTemplate(isolate, exception_constructor);
-    Handle<Map> exception_map = isolate->factory()->NewMap(
-        i::JS_ERROR_TYPE, WasmExceptionPackage::kHeaderSize);
+    Handle<Map> exception_map(isolate->native_context()
+                                  ->wasm_exception_error_function()
+                                  .initial_map(),
+                              isolate);
     Handle<JSObject> exception_proto(
         JSObject::cast(isolate->native_context()
                            ->wasm_exception_error_function()