As a Wayland server KWin does not have to emit additional key repeat
events (unlike X11). The clients are responsible for handling this based
on the provided key repeat information.

Internally KWin needs key repeat, though. E.g. the effects need key
repeat (filtering in Present Windows), window moving by keyboard needs
repeat, etc. etc.

This change introduces the internal key repeat. For each key press a
QTimer is started which gets canceled again on the key release. If the
timer fires it invoked processKey with a new KeyboardKeyAutoRepeat state.
This is handled just like a KeyPress, but states are not updated and
the QKeyEvent has autorepeat set to true.

The event filters check for the autorepeat state and filter the event
out if they are not interested in it. E.g. the filters passing the event
to the Wayland client need to filter it out.

Currently auto-repeat is bound to using libinput. This needs to be
modified. The only backend sending repeated events is X11, thu...