Preload command speedup, Texture/buffer data flush, blit shader fix (#30)

* Move encoder state to be tied to command buffer, so preload and background cbs have their own encoder state

* Texture buffer/data flush, blit shader fix

src/Ryujinx.Graphics.Metal/BackgroundResources.cs

@@ -27,6 +27,7 @@ namespace Ryujinx.Graphics.Metal
             {
                 MTLCommandQueue queue = _renderer.BackgroundQueue;
                 _pool = new CommandBufferPool(queue);
+                _pool.Initialize(null); // TODO: Proper encoder factory for background render/compute
             }
 
             return _pool;