QML: Toolbar keyboard navigation is broken after it is edited

After adding/removing/rearranging controls via 'Toolbar Editor', the keyboard navigation does not work properly. It even sometimes crashes the application.

changed milestone to %Qt redesign (VLC 4.0)

added Component::Interface: Qt label

mentioned in merge request !377 (merged)

closed with commit 829a188d

closed with merge request !377 (merged)

changed milestone to %4.0