LibWeb: Avoid FlyString lookups when setting IDL interface prototypes

This commit introduces a WEB_SET_PROTOTYPE_FOR_INTERFACE macro that
caches the interface name in a local static FlyString. This means that
we only pay for FlyString-from-literal lookup once per browser lifetime
instead of every time the interface is instantiated.

Userland/Libraries/LibWeb/HTML/WorkerNavigator.cpp

@@ -28,7 +28,7 @@ WorkerNavigator::~WorkerNavigator() = default;
 void WorkerNavigator::initialize(JS::Realm& realm)
 {
     Base::initialize(realm);
-    set_prototype(&Bindings::ensure_web_prototype<Bindings::WorkerNavigatorPrototype>(realm, "WorkerNavigator"_fly_string));
+    WEB_SET_PROTOTYPE_FOR_INTERFACE(WorkerNavigator);
 }
 
 }