Fix FPS counter and Game Window speed % breaking on pause/unpause

-Add pause state to FPSCounter.
-Add ability to have more than one "OnStateChanged" callback in core.
-Add GetActualEmulationSpeed() to Core. Returns 1 by default. It's used by my input PRs.

Source/Core/VideoCommon/FPSCounter.h

@@ -11,20 +11,30 @@
 class FPSCounter
 {
 public:
-  // Initializes the FPS counter.
   FPSCounter();
+  ~FPSCounter();
+  FPSCounter(const FPSCounter&) = delete;
+  FPSCounter& operator=(const FPSCounter&) = delete;
+  FPSCounter(FPSCounter&&) = delete;
+  FPSCounter& operator=(FPSCounter&&) = delete;
 
   // Called when a frame is rendered (updated every second).
   void Update();
 
   float GetFPS() const { return m_fps; }
+  double GetDeltaTime() const { return m_time_diff_secs; }
 
 private:
+  void SetPaused(bool paused);
+
   u64 m_last_time = 0;
   u64 m_time_since_update = 0;
+  u64 m_last_time_pause = 0;
   u32 m_frame_counter = 0;
-  float m_fps = 0;
+  int m_on_state_changed_handle = -1;
+  float m_fps = 0.f;
   std::ofstream m_bench_file;
+  double m_time_diff_secs = 0.0;
 
   void LogRenderTimeToFile(u64 val);
 };