Kernel/Mutex: Implemented priority inheritance.

The implementation is based on reverse engineering of the 3DS's kernel.

A mutex holder's priority will be temporarily boosted to the best priority among any threads that want to acquire any of its held mutexes.
When the holder releases the mutex, it's priority will be boosted to the best priority among the threads that want to acquire any of its remaining held mutexes.

src/core/hle/kernel/thread.cpp

@@ -90,9 +90,6 @@ static bool CheckWait_AddressArbiter(const Thread* thread, VAddr wait_address) {
 }
 
 void Thread::Stop() {
-    // Release all the mutexes that this thread holds
-    ReleaseThreadMutexes(this);
-
     // Cancel any outstanding wakeup events for this thread
     CoreTiming::UnscheduleEvent(ThreadWakeupEventType, callback_handle);
     wakeup_callback_handle_table.Close(callback_handle);
@@ -108,6 +105,9 @@ void Thread::Stop() {
 
     WakeupAllWaitingThreads();
 
+    // Release all the mutexes that this thread holds
+    ReleaseThreadMutexes(this);
+
     // Clean up any dangling references in objects that this thread was waiting for
     for (auto& wait_object : wait_objects) {
         wait_object->RemoveWaitingThread(this);