Trigger global shortcuts also on key-repeat

Summary:
Restores feature parity with X11. Global shortcuts need to trigger
also for repeat events. An example is the volume key or screen
brightness.

For other shortcuts like showing yakuake it does not make sense to
trigger on repeat. Thus a long term solution is to add a flag to
global shortcuts whether the key should trigger on repeat.

BUG: 366608

Reviewers: KWin, Plasma on Wayland

Subscribers: plasma-devel, kwin

Tags: Plasma on Wayland, KWin

Differential Revision: https://phabricator.kde.org/D2413