[SyntheticModules] Synthetic Module Export String Fix

This is a very small change which must go in before
https://chromium-review.googlesource.com/c/chromium/src/+/1731108
is able to land.

Certain WPT tests for synthetic modules were spawning DCHECK crashes by JSObject::SetNormalizedProperty.

Export names were previously failing:
DCHECK(name->IsUniqueName());

This small change corrects the issue and allows Module::GetModuleNamespace to run correctly.
This change aligns synthetic module behavior for export string storage with JS modules, as well as the spec.

chromium: 967018
Change-Id: I151e7150290bd72d4e4753c8c5be243eafae915f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1761583Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63264}

src/api/api.cc

@@ -2342,7 +2342,8 @@ Local<Module> Module::CreateSyntheticModule(
   i::Handle<i::FixedArray> i_export_names = i_isolate->factory()->NewFixedArray(
       static_cast<int>(export_names.size()));
   for (int i = 0; i < i_export_names->length(); ++i) {
-    i::Handle<i::String> str = Utils::OpenHandle(*export_names[i]);
+    i::Handle<i::String> str = i_isolate->factory()->InternalizeString(
+        Utils::OpenHandle(*export_names[i]));
     i_export_names->set(i, *str);
   }
   return v8::Utils::ToLocal(