LibWeb: Remove unecessary dependence on Window from DOM and WebIDL

These classes only needed Window to get at its realm. Pass a realm
directly to construct DOM and WebIDL classes.

This change importantly removes the guarantee that a Document will
always have a non-null Window object. Only Documents created by a
BrowsingContext will have a non-null Window object. Documents created by
for example, DocumentFragment, will not have a Window (soon).

This incremental commit leaves some workarounds in place to keep other
parts of the code building.

Userland/Libraries/LibWeb/DOM/HTMLCollection.cpp

@@ -5,10 +5,10 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <LibWeb/Bindings/Intrinsics.h>
 #include <LibWeb/DOM/Element.h>
 #include <LibWeb/DOM/HTMLCollection.h>
 #include <LibWeb/DOM/ParentNode.h>
-#include <LibWeb/HTML/Window.h>
 #include <LibWeb/Namespace.h>
 
 namespace Web::DOM {
@@ -19,7 +19,7 @@ JS::NonnullGCPtr<HTMLCollection> HTMLCollection::create(ParentNode& root, Functi
 }
 
 HTMLCollection::HTMLCollection(ParentNode& root, Function<bool(Element const&)> filter)
-    : LegacyPlatformObject(root.window().cached_web_prototype("HTMLCollection"))
+    : LegacyPlatformObject(Bindings::cached_web_prototype(root.realm(), "HTMLCollection"))
     , m_root(root)
     , m_filter(move(filter))
 {