Handle keyboard in action selector OSD
Summary:
The OSD is not all that bad, but it was only usable with the mouse.
Change it so that left-right and tab navigates and space/return confirms
the selection.
BUG: 395804
Reviewers: Plasma, davidedmundson
Subscribers: broulik, davidedmundson, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D14165