LibWebView: Define the list of built-in search engines in LibWebView

These engines and their query URLs are duplicated in several places.
Before implementing search support in the AppKit chrome, let's move
these engines to LibWebView.

Userland/Libraries/LibWebView/SearchEngine.h

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Span.h>
+#include <AK/StringView.h>
+
+namespace WebView {
+
+struct SearchEngine {
+    StringView name;
+    StringView query_url;
+};
+
+ReadonlySpan<SearchEngine> search_engines();
+SearchEngine const& default_search_engine();
+Optional<SearchEngine const&> find_search_engine(StringView name);
+
+}