Ladybird+LibWebView: Move CookieJar, Database, and History to LibWebView

These classes are used as-is in all chromes. Move them to LibWebView so
that non-Serenity chromes don't have to awkwardly reach into its headers
and sources.

Userland/Libraries/LibWebView/Forward.h

@@ -6,11 +6,25 @@
 
 #pragma once
 
+#include <AK/Traits.h>
+
 namespace WebView {
 
 class ConsoleClient;
+class CookieJar;
+class Database;
+class History;
 class OutOfProcessWebView;
 class ViewImplementation;
 class WebContentClient;
 
+struct CookieStorageKey;
+
+}
+
+namespace AK {
+
+template<>
+struct Traits<WebView::CookieStorageKey>;
+
 }