LibCore+Ladybird: Don't force timer ids to be integer just to remap them

If we don't force event loop to fit timer id into integer, we can
eliminate awkward IDAllocator inside EventLoopImplementations.

Userland/Libraries/LibCore/EventReceiver.h

@@ -169,7 +169,7 @@ protected:
 private:
     EventReceiver* m_parent { nullptr };
     ByteString m_name;
-    int m_timer_id { 0 };
+    intptr_t m_timer_id { 0 };
     Vector<NonnullRefPtr<EventReceiver>> m_children;
     Function<bool(Core::Event&)> m_event_filter;
 };