Kernel: destruct thread/timer managers after processes (#4399)

Processes can keep some Thread/Timer object alive while the manager is already destructed, resulting use-after-free in Thread::Stop and Timer::dtor. To resolve this, the manager objects should be destructed after all related object destructed.
Fixes a bug where quiting citra causes crash while the game is using a Timer.

src/core/hle/kernel/kernel.h

@@ -228,6 +228,9 @@ private:
     std::unique_ptr<ResourceLimitList> resource_limits;
     std::atomic<u32> next_object_id{0};
 
+    std::unique_ptr<ThreadManager> thread_manager;
+    std::unique_ptr<TimerManager> timer_manager;
+
     // TODO(Subv): Start the process ids from 10 for now, as lower PIDs are
     // reserved for low-level services
     u32 next_process_id = 10;
@@ -237,9 +240,6 @@ private:
 
     SharedPtr<Process> current_process;
 
-    std::unique_ptr<ThreadManager> thread_manager;
-    std::unique_ptr<TimerManager> timer_manager;
-
     std::unique_ptr<ConfigMem::Handler> config_mem_handler;
     std::unique_ptr<SharedPage::Handler> shared_page_handler;
 };