Please implement functionality for the app bar (feature)

[bksubhuti]

I was not able to make this work on an appbar as an action[].
I get the speed dial button and animations, but the children menu items do not show up.
So I had to implement my own PopupMenuButton. It would be good if this worked inside the appbar.

 Widget build(BuildContext context) {
    return AppBar(
      automaticallyImplyLeading: false,
      title: Text(AppLocalizations.of(context)!.bookmark),
      actions: [
        buildDropdownButton(context),