Let the Renderer decide when to exit fullscreen.

This ensures the transition from/to exclusive mode happens while the RenderFrame is fullscreen.

This prevents fullscreen loops and relieves us of having to restore the window size after we exit fullscreen.

Source/Core/VideoBackends/D3D/D3DBase.cpp

@@ -440,9 +440,6 @@ void Reset()
 	// release all back buffer references
 	SAFE_RELEASE(backbuf);
 
-	// apply fullscreen state
-	D3D::swapchain->SetFullscreenState(g_ActiveConfig.bFullscreen, nullptr);
-
 	// resize swapchain buffers
 	RECT client;
 	GetClientRect(hWnd, &client);