kbd-state: add keyboard state tracker

kbd-state: add keyboard state tracker

Now that most user interfaces are using QKeyCodes it is easier to have
common keyboard code useable by all user interfaces.

This patch adds helper code to track the state of all keyboard keys,
using a bitmap indexed by QKeyCode.  Modifier state is tracked too,
as separate bitmap.  That makes checking modifier state easier.
Likewise we can easily apply special handling for capslock & numlock
(toggles on keypress) and ctrl + shift (we have two keys for that).

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 20190122092814.14919-2-kraxel@redhat.com

[ kraxel: added license boilerplate header ]

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>