LibJS+LibWeb: Another round of bringing module loading closer to spec

In particular, this patch focuses on:
- Updating the old "import assertions" to the new "import attributes"
- Allowing realms as module import referrer

Userland/Libraries/LibJS/ModuleLoading.h

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2023, networkException <networkexception@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Variant.h>
+#include <LibJS/Forward.h>
+#include <LibJS/Heap/GCPtr.h>
+
+namespace JS {
+
+using ImportedModuleReferrer = Variant<NonnullGCPtr<Script>, NonnullGCPtr<CyclicModule>, NonnullGCPtr<Realm>>;
+using ImportedModulePayload = Variant<NonnullGCPtr<GraphLoadingState>, NonnullGCPtr<PromiseCapability>>;
+
+}