kernel/thread: Change owner_process to std::weak_ptr (#5325)

* kernel/thread: Change owner_process to std::weak_ptr

Previously this leaked almost all kernel objects. In short, Threads own Processes which own HandleTables which own maps of Objects which include Threads.

Changing this to weak_ptr at least got the camera interfaces to destruct properly. Did not really check the other objects though, and I think there are probably more leaks.

* hle/kernel: Lock certain objects while deserializing

When deserializing other kernel objects, these objects (`MemoryRegion`s and `VMManager`s) can possibly get modified. To avoid inconsistent state caused by destructor side-effects, we may as well simply lock them until loading is fully completed.

* Fix silly typo

Somehow this didn't break?!

src/core/hle/kernel/hle_ipc.cpp

@@ -29,7 +29,9 @@ public:
             callback->WakeUp(thread, *context, reason);
         }
 
-        auto& process = thread->owner_process;
+        auto process = thread->owner_process.lock();
+        ASSERT(process);
+
         // We must copy the entire command buffer *plus* the entire static buffers area, since
         // the translation might need to read from it in order to retrieve the StaticBuffer
         // target addresses.