Describe the bug
The DropDownButton's itemClick event doesn't work when you select one of its items with a tap on a touchpad.

To Reproduce

1. Open this StackBlitz example
2. Expand the DropDownButton and select an item with a mouse click - the itemClick event is logged in the event logger
3. Using a touchpad, select an item by tapping on the touchpad.
4. See the event logger - the itemClick event is not logged

Expected behavior
The itemClick event should be triggered consistently no matter if a mouse click or touchpad is used