LibWeb: Use cached_web_prototype() as much as possible

Unlike ensure_web_prototype<T>(), the cached version doesn't require the
prototype type to be fully formed, so we can use it without including
the FooPrototype.h header. It's also a bit less verbose. :^)

Userland/Libraries/LibWeb/HTML/HTMLButtonElement.cpp

@@ -4,7 +4,6 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <LibWeb/Bindings/HTMLButtonElementPrototype.h>
 #include <LibWeb/DOM/Document.h>
 #include <LibWeb/HTML/HTMLButtonElement.h>
 #include <LibWeb/HTML/HTMLFormElement.h>
@@ -14,7 +13,7 @@ namespace Web::HTML {
 HTMLButtonElement::HTMLButtonElement(DOM::Document& document, DOM::QualifiedName qualified_name)
     : HTMLElement(document, move(qualified_name))
 {
-    set_prototype(&window().ensure_web_prototype<Bindings::HTMLButtonElementPrototype>("HTMLButtonElement"));
+    set_prototype(&window().cached_web_prototype("HTMLButtonElement"));
 
     // https://html.spec.whatwg.org/multipage/form-elements.html#the-button-element:activation-behaviour
     activation_behavior = [this](auto&) {