kern: implement process exit

libraries/libmesosphere/include/mesosphere/kern_k_thread.hpp

@@ -448,6 +448,9 @@ namespace ams::kern {
             Result Run();
             void Exit();
 
+            void Terminate();
+            ThreadState RequestTerminate();
+
             Result Sleep(s64 timeout);
 
             ALWAYS_INLINE void *GetStackTop() const { return reinterpret_cast<StackParameters *>(this->kernel_stack_top) - 1; }