LibWeb+Meta: Add wrapper for the BufferSource/ArrayBufferView IDL types

These wrappers will make it much easier to do various operations on the
different ArrayBuffer-related classes in LibWeb compared to the current
solution, which is to just accept a Handle<Object> everywhere (and use
"any" in the *.idl files).

Co-Authored-By: Matthew Olsson <mattco@serenityos.org>

Userland/Libraries/LibWeb/Forward.h

@@ -678,6 +678,8 @@ class WebGLRenderingContextBase;
 }
 
 namespace Web::WebIDL {
+class ArrayBufferView;
+class BufferSource;
 class CallbackType;
 class DOMException;