LibWeb: Implement the JS host hooks for promises, job callbacks and more

This overrides the JS host hooks to follow the spec for queuing
promises, making/calling job callbacks, unhandled promise rejection
handling and FinalizationRegistry queuing.

This also allows us to drop the on_call_stack_emptied hook in
Document::interpreter().

Userland/Libraries/LibWeb/HTML/EventLoop/Task.h

@@ -26,6 +26,7 @@ public:
         PostedMessage,
         Microtask,
         TimerTask,
+        JavaScriptEngine,
     };
 
     static NonnullOwnPtr<Task> create(Source source, DOM::Document* document, Function<void()> steps)