Add a callback to execute whenever there are no higher priority events pending

Property definitions

gtk :: gdk $ Sys :: gdk_threads_add_idle
# Add a callback to execute whenever there are no higher priority events pending
fun gdk_threads_add_idle(task: Task): Int import Task.gdk_main `{
	Task_incr_ref(task);
	return gdk_threads_add_idle(&nit_gdk_callback_task, task);
`}
lib/gtk/v3_4/gdk.nit:42,1--46,2