[DesktopView] Move cancelling showing desktop into keyPressEvent

Authored by broulik on Aug 31 2017, 3:13 PM.

Description

[DesktopView] Move cancelling showing desktop into keyPressEvent

This will route the event through the containment first which can then intercept it, e.g. to prevent
Escape from exiting showing desktop while renaming where it should only cancel that.

CCBUG: 352988

Differential Revision: https://phabricator.kde.org/D7630