Add per-handler LED state and a NotifierList for UI backends to
subscribe to LED changes.
Devices call qemu_input_handler_set_led() to store their LED state and
notify backends. Notify also on focus change, or list update.
Note: I considered conflating mouse-mode & led-state changes, but those
are quite different events (from different source kinds etc) and we may
want to improve the internal implementation.
Reviewed-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
63cdb870aa