VideoBackends: Combine Initialize/Prepare and Cleanup/Shutdown methods

Also allows the work previously done in Prepare to return a failure
status.

Source/Core/VideoBackends/Null/NullBackend.cpp

@@ -58,38 +58,32 @@ bool VideoBackend::Initialize(void* window_handle)
   InitializeShared();
   InitBackendInfo();
 
-  return true;
-}
-
-// This is called after Initialize() from the Core
-// Run from the graphics thread
-void VideoBackend::Video_Prepare()
-{
   g_renderer = std::make_unique<Renderer>();
   g_vertex_manager = std::make_unique<VertexManager>();
   g_perf_query = std::make_unique<PerfQuery>();
   g_framebuffer_manager = std::make_unique<FramebufferManagerBase>();
   g_texture_cache = std::make_unique<TextureCache>();
+
   VertexShaderCache::s_instance = std::make_unique<VertexShaderCache>();
   GeometryShaderCache::s_instance = std::make_unique<GeometryShaderCache>();
   PixelShaderCache::s_instance = std::make_unique<PixelShaderCache>();
+  return true;
 }
 
 void VideoBackend::Shutdown()
 {
-  ShutdownShared();
-}
+  g_renderer->Shutdown();
 
-void VideoBackend::Video_Cleanup()
-{
-  CleanupShared();
   PixelShaderCache::s_instance.reset();
   VertexShaderCache::s_instance.reset();
   GeometryShaderCache::s_instance.reset();
+
   g_texture_cache.reset();
   g_perf_query.reset();
   g_vertex_manager.reset();
   g_framebuffer_manager.reset();
   g_renderer.reset();
+
+  ShutdownShared();
 }
 }