LibWeb: Correctly initialize Storage objects on the Document

Instead of storing all storage objects in static memory, we now
follow the the spec by lazily creating a unique Storage object
on each document object.

Each Storage object now holds a 'proxy' to the underlying backing
storage. For now, this proxy is simply a reference to the backing
object. In the future, it will need to be some type of interface
object that stores on a SQLite database or similar.

Session storage is now correctly stored / tracked as part of the
TraversableNavigable object.

Local storage is still stored in a static map, but eventually this
should be factored into something that is stored at the user agent
level.

Libraries/LibWeb/StorageAPI/StorageBottle.cpp

@@ -0,0 +1,88 @@
+/*
+ * Copyright (c) 2024-2025, Shannon Booth <shannon@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/HTML/Scripting/Environments.h>
+#include <LibWeb/HTML/TraversableNavigable.h>
+#include <LibWeb/HTML/Window.h>
+#include <LibWeb/StorageAPI/StorageBottle.h>
+#include <LibWeb/StorageAPI/StorageEndpoint.h>
+#include <LibWeb/StorageAPI/StorageShed.h>
+
+namespace Web::StorageAPI {
+
+StorageBucket::StorageBucket(StorageType type)
+{
+    // 1. Let bucket be null.
+    // 2. If type is "local", then set bucket to a new local storage bucket.
+    // 3. Otherwise:
+    //     1. Assert: type is "session".
+    //     2. Set bucket to a new session storage bucket.
+
+    // 4. For each endpoint of registered storage endpoints whose types contain type, set bucket’s bottle map[endpoint’s identifier] to a new storage bottle whose quota is endpoint’s quota.
+    for (auto const& endpoint : StorageEndpoint::registered_endpoints()) {
+        if (endpoint.type == type)
+            bottle_map.set(endpoint.identifier, StorageBottle::create(endpoint.quota));
+    }
+
+    // 5. Return bucket.
+}
+
+// https://storage.spec.whatwg.org/#obtain-a-storage-bottle-map
+RefPtr<StorageBottle> obtain_a_storage_bottle_map(StorageType type, HTML::EnvironmentSettingsObject& environment, StringView identifier)
+{
+    // 1. Let shed be null.
+    StorageShed* shed = nullptr;
+
+    // 2. If type is "local", then set shed to the user agent’s storage shed.
+    if (type == StorageType::Local) {
+        shed = &user_agent_storage_shed();
+    }
+    // 3. Otherwise:
+    else {
+        // 1. Assert: type is "session".
+        VERIFY(type == StorageType::Session);
+
+        // 2. Set shed to environment’s global object’s associated Document’s node navigable’s traversable navigable’s storage shed.
+        shed = &verify_cast<HTML::Window>(environment.global_object()).associated_document().navigable()->traversable_navigable()->storage_shed();
+    }
+
+    // 4. Let shelf be the result of running obtain a storage shelf, with shed, environment, and type.
+    VERIFY(shed);
+    auto shelf = shed->obtain_a_storage_shelf(environment, type);
+
+    // 5. If shelf is failure, then return failure.
+    if (!shelf.has_value())
+        return {};
+
+    // 6. Let bucket be shelf’s bucket map["default"].
+    auto& bucket = shelf->bucket_map.get("default"sv).value();
+
+    // 7. Let bottle be bucket’s bottle map[identifier].
+    auto bottle = bucket.bottle_map.get(identifier).value();
+
+    // 8. Let proxyMap be a new storage proxy map whose backing map is bottle’s map.
+    // 9. Append proxyMap to bottle’s proxy map reference set.
+    // 10. Return proxyMap.
+    return bottle->proxy();
+}
+
+// https://storage.spec.whatwg.org/#obtain-a-session-storage-bottle-map
+RefPtr<StorageBottle> obtain_a_session_storage_bottle_map(HTML::EnvironmentSettingsObject& environment, StringView identifier)
+{
+    // To obtain a session storage bottle map, given an environment settings object environment and storage identifier identifier,
+    // return the result of running obtain a storage bottle map with "session", environment, and identifier.
+    return obtain_a_storage_bottle_map(StorageType::Session, environment, identifier);
+}
+
+// https://storage.spec.whatwg.org/#obtain-a-local-storage-bottle-map
+RefPtr<StorageBottle> obtain_a_local_storage_bottle_map(HTML::EnvironmentSettingsObject& environment, StringView identifier)
+{
+    // To obtain a local storage bottle map, given an environment settings object environment and storage identifier identifier,
+    // return the result of running obtain a storage bottle map with "local", environment, and identifier.
+    return obtain_a_storage_bottle_map(StorageType::Local, environment, identifier);
+}
+
+}