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/Geometry/DOMPoint.cpp

@@ -34,7 +34,7 @@ DOMPoint::~DOMPoint() = default;
 void DOMPoint::initialize(JS::Realm& realm)
 {
     Base::initialize(realm);
-    set_prototype(&Bindings::ensure_web_prototype<Bindings::DOMPointPrototype>(realm, "DOMPoint"_fly_string));
+    WEB_SET_PROTOTYPE_FOR_INTERFACE(DOMPoint);
 }
 
 }