[Kernel] Improved TUs Support

- Changed name of config option to apply_title_update to better reflect what that option does
- Mount TU package to UPDATE: partition
- Simplified UserModule::title_id()
- Splitted loading module into two parts to allow applying TUs and custom patches

src/xenia/kernel/kernel_state.h

@@ -134,6 +134,8 @@ class KernelState {
   void SetExecutableModule(object_ref<UserModule> module);
   object_ref<UserModule> LoadUserModule(const std::string_view name,
                                         bool call_entry = true);
+  X_RESULT FinishLoadingUserModule(const object_ref<UserModule> module,
+                                   bool call_entry = true);
   void UnloadUserModule(const object_ref<UserModule>& module,
                         bool call_entry = true);
 
@@ -150,6 +152,7 @@ class KernelState {
     return object_ref<T>(reinterpret_cast<T*>(module.release()));
   }
 
+  X_RESULT ApplyTitleUpdate(const object_ref<UserModule> module);
   // Terminates a title: Unloads all modules, and kills all guest threads.
   // This DOES NOT RETURN if called from a guest thread!
   void TerminateTitle();