Kernel: Break out of the idle loop on WaitQueue wake instead of on IRQ

Now that we have proper wait queues to drive waiter wakeup, we can use
the wake actions to break out of the scheduler's idle loop when we've
got a thread to run.

Kernel/WaitQueue.cpp

@@ -22,6 +22,7 @@ void WaitQueue::wake_one()
         return;
     if (auto* thread = m_threads.take_first())
         thread->wake_from_queue();
+    Scheduler::stop_idling();
 }
 
 void WaitQueue::wake_all()
@@ -31,4 +32,5 @@ void WaitQueue::wake_all()
         return;
     while (!m_threads.is_empty())
         m_threads.take_first()->wake_from_queue();
+    Scheduler::stop_idling();
 }