TextureCache: Refactor with smart pointers

The whole ownership model was getting a bit of a mess, with a some
of special cases to deal with. And I'm planning to make it even more
complex in the future.
So here is some upfront work to convert it over to reference counted
pointers.

Source/Core/VideoCommon/VideoBackendBase.cpp

@@ -44,6 +44,7 @@
 #include "VideoCommon/CPMemory.h"
 #include "VideoCommon/CommandProcessor.h"
 #include "VideoCommon/Fifo.h"
+#include "VideoCommon/FramebufferManager.h"
 #include "VideoCommon/GeometryShaderManager.h"
 #include "VideoCommon/IndexGenerator.h"
 #include "VideoCommon/OpcodeDecoding.h"
@@ -339,6 +340,20 @@ void VideoBackendBase::InitializeShared()
 
 void VideoBackendBase::ShutdownShared()
 {
+  if (g_shader_cache)
+    g_shader_cache->Shutdown();
+  if (g_renderer)
+    g_renderer->Shutdown();
+  if (g_texture_cache)
+    g_texture_cache->Shutdown();
+
+  g_perf_query.reset();
+  g_texture_cache.reset();
+  g_framebuffer_manager.reset();
+  g_shader_cache.reset();
+  g_vertex_manager.reset();
+  g_renderer.reset();
+
   m_initialized = false;
 
   auto& system = Core::System::GetInstance();