Remove no-parent-event prop for ui.menu

[falkoschindler]

Description

Originally we misunderstood the QMenu API and placed the menu element next to its trigger button:

with ui.row():
    with ui.menu() as menu:
        ui.menu_item('One')
        ui.menu_item('Two')
    ui.button('Menu', on_click=menu.open)
    ui.label('Another element')

This works, but opens the menu event when clicking on "Another element" (or any other element in the row). To prevent that, we set the prop "no-parent-event".

But the correct way to use a QMenu is to wrap it with the trigger button:

with ui.row():
    with ui.button('Menu', on_click=lambda: menu.open()):
        with ui.menu() as menu:
            ui.menu_item('One')
            ui.menu_item('Two')
    ui.label('Another element')

This makes the "no-parent-event" prop ineffective and it can be removed.
Removing "no-parent-event", i.e. activating the parent event for ui.menu even allows removing the button click handler. A button click will automatically open the menu. In short:

with ui.button('Menu'):
    with ui.menu() as menu:
        ui.menu_item('One')
        ui.menu_item('Two')

I think this is very nice. And it's closer to how Quasar works by default. Therefore we want to remove the "no-parent-event" prop. Since it is a braking change, we schedule it for the 1.3.0 release.