Add support for shader constant buffer slot indexing (#1608)

* Add support for shader constant buffer slot indexing

* Fix typo

Ryujinx.Graphics.Shader/Decoders/CbIndexMode.cs

@@ -0,0 +1,10 @@
+namespace Ryujinx.Graphics.Shader.Decoders
+{
+    enum CbIndexMode
+    {
+        Default = 0,
+        Il      = 1,
+        Is      = 2,
+        Isl     = 3
+    }
+}