Consistent arrow key handling in the Informative Alt+Tab skin

Authored by Zren on Jan 18 2019, 5:44 PM.

Description

Consistent arrow key handling in the Informative Alt+Tab skin

Moved Dialog.Keys.onPressed to Dialog.mainItem.Keys.onPressed so
that all tabbox skins are consistent. This fixes up/down arrow key
navigation in this skin.

CCBUG: 370185

Differential Revision: https://phabricator.kde.org/D16093