Core, VideoCommon: Fix crash at shutdown due to destructor ordering

Previously, PerformanceTracker registered a callback to be updated on
emulation state changes. PerformanceTrackers live in a global variable
(g_perf_metrics) within libvideocommon. The callback was stored in a
global variable in libcore. This created a race condition at shutdown
between these libraries, when the PerfTracker's destructor tried to
unregister the callback.
Notify the PerfTracker directly from libcore, without callbacks, since
Core.cpp already references g_perf_metrics explicitly. Also rename
Core::CallOnStateChangedCallbacks to NotifyStateChanged to better
reflect what it's doing.

Source/Core/VideoCommon/PerformanceMetrics.cpp

@@ -35,6 +35,12 @@ void PerformanceMetrics::CountVBlank()
   m_vps_counter.Count();
 }
 
+void PerformanceMetrics::OnEmulationStateChanged([[maybe_unused]] Core::State state)
+{
+  m_fps_counter.InvalidateLastTime();
+  m_vps_counter.InvalidateLastTime();
+}
+
 void PerformanceMetrics::CountThrottleSleep(DT sleep)
 {
   m_time_sleeping += sleep;