LibWeb: Stub out the PerformanceTiming object from Navigation Timing

Just have all the timing functions return 0 for now.

We can now run the Shynet JS on https://linus.dev/ although the XHR
is rejected by our same-origin policy.

Userland/Libraries/LibWeb/HighResolutionTime/Performance.cpp

@@ -36,6 +36,7 @@ namespace Web::HighResolutionTime {
 Performance::Performance(DOM::Window& window)
     : DOM::EventTarget(static_cast<Bindings::ScriptExecutionContext&>(window.document()))
     , m_window(window)
+    , m_timing(make<NavigationTiming::PerformanceTiming>(window))
 {
     m_timer.start();
 }