LibJS+LibWeb: Pass prototype to Object constructor

Everyone who constructs an Object must now pass a prototype object when
applicable. There's still a fair amount of code that passes something
fetched from the Interpreter, but this brings us closer to being able
to detach prototypes from Interpreter eventually.

Libraries/LibJS/Runtime/Date.cpp

@@ -38,7 +38,8 @@ Date* Date::create(GlobalObject& global_object, Core::DateTime datetime, u16 mil
 }
 
 Date::Date(Core::DateTime datetime, u16 milliseconds, Object& prototype)
-    : m_datetime(datetime)
+    : Object(&prototype)
+    , m_datetime(datetime)
     , m_milliseconds(milliseconds)
 {
     set_prototype(&prototype);