Move PerformanceMetrics from global variable to System

This avoids the static initialization order fiasco between Core and VideoCommon

Co-authored-by: Jordan Woyak <[email protected]>

Source/Core/Core/HW/VideoInterface.cpp

@@ -895,7 +895,7 @@ void VideoInterfaceManager::EndField(FieldType field, u64 ticks)
   if (is_vblank_data_wanted)
     m_system.GetCoreTiming().Throttle(ticks);
 
-  g_perf_metrics.CountVBlank();
+  m_system.GetPerfMetrics().CountVBlank();
   m_system.GetVideoEvents().vi_end_field_event.Trigger();
   Core::OnFrameEnd(m_system);
 }