Everywhere: Implement persistence of localStorage using sqlite

This change follows the pattern of our cookies persistence
implementation: the "browser" process is responsible for interacting
with the sqlite database, and WebContent communicates all storage
operations via IPC.

The new database table uses (storage_endpoint, storage_key, bottle_key)
as the primary key. This design follows concepts from the
https://storage.spec.whatwg.org/ and is intended to support reuse of the
persistence layer for other APIs (e.g., CacheStorage, IndexedDB). For
now, `storage_endpoint` is always "localStorage", `storage_key` is the
website's origin, and `bottle_key` is the name of the localStorage key.

Libraries/LibWebView/StorageJar.h

@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) 2025, Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/HashMap.h>
+#include <AK/String.h>
+#include <AK/Traits.h>
+#include <LibWeb/StorageAPI/StorageEndpoint.h>
+#include <LibWebView/Database.h>
+#include <LibWebView/Forward.h>
+#include <LibWebView/StorageOperationError.h>
+
+namespace WebView {
+
+using StorageEndpointType = Web::StorageAPI::StorageEndpointType;
+
+struct StorageLocation {
+    bool operator==(StorageLocation const&) const = default;
+
+    StorageEndpointType storage_endpoint;
+    String storage_key;
+    String bottle_key;
+};
+
+class StorageJar {
+    AK_MAKE_NONCOPYABLE(StorageJar);
+    AK_MAKE_NONMOVABLE(StorageJar);
+
+public:
+    static ErrorOr<NonnullOwnPtr<StorageJar>> create(Database&);
+    static NonnullOwnPtr<StorageJar> create();
+
+    ~StorageJar();
+
+    Optional<String> get_item(StorageEndpointType storage_endpoint, String const& storage_key, String const& bottle_key);
+    StorageOperationError set_item(StorageEndpointType storage_endpoint, String const& storage_key, String const& bottle_key, String const& bottle_value);
+    void remove_item(StorageEndpointType storage_endpoint, String const& storage_key, String const& key);
+    void clear_storage_key(StorageEndpointType storage_endpoint, String const& storage_key);
+    Vector<String> get_all_keys(StorageEndpointType storage_endpoint, String const& storage_key);
+
+private:
+    struct Statements {
+        Database::StatementID set_item { 0 };
+        Database::StatementID delete_item { 0 };
+        Database::StatementID get_item { 0 };
+        Database::StatementID clear { 0 };
+        Database::StatementID get_keys { 0 };
+        Database::StatementID calculate_size_excluding_key { 0 };
+    };
+
+    class TransientStorage {
+    public:
+        StorageOperationError set_item(StorageLocation const& key, String const& value);
+        Optional<String> get_item(StorageLocation const& key);
+        void delete_item(StorageLocation const& key);
+        void clear(StorageEndpointType storage_endpoint, String const& storage_key);
+        Vector<String> get_keys(StorageEndpointType storage_endpoint, String const& storage_key);
+
+    private:
+        HashMap<StorageLocation, String> m_storage_items;
+    };
+
+    struct PersistedStorage {
+        StorageOperationError set_item(StorageLocation const& key, String const& value);
+        Optional<String> get_item(StorageLocation const& key);
+        void delete_item(StorageLocation const& key);
+        void clear(StorageEndpointType storage_endpoint, String const& storage_key);
+        Vector<String> get_keys(StorageEndpointType storage_endpoint, String const& storage_key);
+
+        Database& database;
+        Statements statements;
+    };
+
+    explicit StorageJar(Optional<PersistedStorage>);
+
+    Optional<PersistedStorage> m_persisted_storage;
+    TransientStorage m_transient_storage;
+};
+
+}
+
+template<>
+struct AK::Traits<WebView::StorageLocation> : public AK::DefaultTraits<WebView::StorageLocation> {
+    static unsigned hash(WebView::StorageLocation const& key)
+    {
+        unsigned hash = 0;
+        hash = pair_int_hash(hash, to_underlying(key.storage_endpoint));
+        hash = pair_int_hash(hash, key.storage_key.hash());
+        hash = pair_int_hash(hash, key.bottle_key.hash());
+        return hash;
+    }
+};