Core: Assert that only the Host thread may call PauseAndLock().

Source/Core/Core/Core.h

@@ -132,6 +132,8 @@ void DeclareAsCPUThread();
 void UndeclareAsCPUThread();
 void DeclareAsGPUThread();
 void UndeclareAsGPUThread();
+void DeclareAsHostThread();
+void UndeclareAsHostThread();
 
 std::string StopMessage(bool main_thread, std::string_view message);
 
@@ -140,6 +142,7 @@ bool IsRunningAndStarted();       // is running and the CPU loop has been entere
 bool IsRunningInCurrentThread();  // this tells us whether we are running in the CPU thread.
 bool IsCPUThread();               // this tells us whether we are the CPU thread.
 bool IsGPUThread();
+bool IsHostThread();
 
 bool WantsDeterminism();