Revert "Revert the Metal Experiment (#701)"

This reverts commit fe1617ffea.

src/Ryujinx.Graphics.Metal/Effects/IPostProcessingEffect.cs

@@ -0,0 +1,10 @@
+using System;
+
+namespace Ryujinx.Graphics.Metal.Effects
+{
+    internal interface IPostProcessingEffect : IDisposable
+    {
+        const int LocalGroupSize = 64;
+        Texture Run(Texture view, int width, int height);
+    }
+}