Kernel: Move WaitObject to a separate file

Now that HandleTable doesn't directly depend on WaitObject anymore, this
can be separated from the main kernel.h header.

src/citra_qt/debugger/wait_tree.cpp

@@ -10,6 +10,7 @@
 #include "core/hle/kernel/semaphore.h"
 #include "core/hle/kernel/thread.h"
 #include "core/hle/kernel/timer.h"
+#include "core/hle/kernel/wait_object.h"
 
 WaitTreeItem::~WaitTreeItem() {}
 

src/citra_qt/debugger/wait_tree.h

@@ -4,12 +4,10 @@
 
 #pragma once
 
-#include <boost/container/flat_set.hpp>
-
 #include <QAbstractItemModel>
 #include <QDockWidget>
 #include <QTreeView>
-
+#include <boost/container/flat_set.hpp>
 #include "core/core.h"
 #include "core/hle/kernel/kernel.h"