kernel: Move object class to its own source files

General moving to keep kernel object types separate from the direct
kernel code. Also essentially a preliminary cleanup before eliminating
global kernel state in the kernel code.

src/core/hle/kernel/scheduler.h

@@ -8,6 +8,7 @@
 #include <vector>
 #include "common/common_types.h"
 #include "common/thread_queue_list.h"
+#include "core/hle/kernel/object.h"
 #include "core/hle/kernel/thread.h"
 
 class ARM_Interface;