Implement Geometry shaders (#280)

* Implement Geometry shaders

* Add EmitVertex() and EndPrimitive()

* Read output geometry data from header

* Stub Vmad

* Add Iadd_I32

* Stub Mov_S (S2R)

* Stub Isberd

* Change vertex index to gpr39 in Abuf

* Add stub messages for consistency

* Do not print input block when there is no attributes

* Use GL_ARB_enhanced_layouts

* Skip geometry shaders when there's no GL_ARB_enhanced_layouts

* Address feedback

* Address feedback

Ryujinx.Graphics/Gal/OpenGL/OGLExtension.cs

@@ -0,0 +1,43 @@
+using OpenTK.Graphics.OpenGL;
+
+namespace Ryujinx.Graphics.Gal.OpenGL
+{
+    static class OGLExtension
+    {
+        private static bool Initialized = false;
+
+        private static bool EnhancedLayouts;
+
+        public static bool HasEnhancedLayouts()
+        {
+            EnsureInitialized();
+
+            return EnhancedLayouts;
+        }
+
+        private static void EnsureInitialized()
+        {
+            if (Initialized)
+            {
+                return;
+            }
+
+            EnhancedLayouts = HasExtension("GL_ARB_enhanced_layouts");
+        }
+
+        private static bool HasExtension(string Name)
+        {
+            int NumExtensions = GL.GetInteger(GetPName.NumExtensions);
+
+            for (int Extension = 0; Extension < NumExtensions; Extension++)
+            {
+                if (GL.GetString(StringNameIndexed.Extensions, Extension) == Name)
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+    }
+}