DolphinQt: Properly lock CPU before accessing emulated memory

This fixes a problem I was having where using frame advance with the
debugger open would frequently cause panic alerts about invalid addresses
due to the CPU thread changing MSR.DR while the host thread was trying
to access memory.

To aid in tracking down all the places where we weren't properly locking
the CPU, I've created a new type (in Core.h) that you have to pass as a
reference or pointer to functions that require running as the CPU thread.

Source/Core/Core/ConfigManager.h

@@ -16,6 +16,11 @@
 
 class IniFile;
 
+namespace Core
+{
+class CPUThreadGuard;
+}
+
 namespace DiscIO
 {
 enum class Language;
@@ -68,7 +73,7 @@ struct SConfig
   void SetRunningGameMetadata(const std::string& game_id);
   // Reloads title-specific map files, patches, custom textures, etc.
   // This should only be called after the new title has been loaded into memory.
-  static void OnNewTitleLoad();
+  static void OnNewTitleLoad(const Core::CPUThreadGuard& guard);
 
   void LoadDefaults();
   static std::string MakeGameID(std::string_view file_name);