LibWeb: Implement navigator.{plugins,mimeTypes}

Author: https://github.com/Lubrsi
Commit: 4d0277cd9a
Pull-request: https://github.com/SerenityOS/serenity/pull/17658
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibWeb/Forward.h

@@ -328,11 +328,15 @@ class Location;
 class MessageChannel;
 class MessageEvent;
 class MessagePort;
+class MimeType;
+class MimeTypeArray;
 struct NavigationParams;
 class Navigator;
 class Origin;
 class PageTransitionEvent;
 class Path2D;
+class Plugin;
+class PluginArray;
 struct PolicyContainer;
 class PromiseRejectionEvent;
 class WorkerDebugConsoleClient;