Use Meta+D to Show Desktop by default
Summary: Bind the keyboard shortcut Meta+D to Show Desktop.
Test Plan:
Apply patch, compile KWin, do kwin --replace, reset KWin shortcuts to default values if you've previously changed the Show Desktop's keyboard shortcut
Meta+D now shows and hides the desktop.
Reviewers: KWin, zzag
Reviewed By: KWin, zzag
Subscribers: filipf, abetts, zzag, kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D20066