LibWebView: Add a helper to sanitize a user-provided URL

We currently implement several forms of this method across the Ladybird
chromes. As such, we see commits to add special URL handling that only
affects a single chrome. Instead, let's consolidate all special handling
in a single location for all chromes to make use of.

This method can handle resolving file:// URLs, falling back to a search
engine query, and validation against the Public Suffix List. These cases
were gathered from the various chromes.

Userland/Libraries/LibWebView/URL.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Optional.h>
+#include <AK/StringView.h>
+#include <AK/URL.h>
+
+namespace WebView {
+
+enum class AppendTLD {
+    No,
+    Yes,
+};
+
+Optional<URL> sanitize_url(StringView, Optional<StringView> search_engine = {}, AppendTLD = AppendTLD::No);
+
+}