Merge pull request #1461 from Unity-Technologies/sg/fix-screen-position

Fix ScreenPosition transformation

com.unity.shadergraph/Editor/Data/Util/ShaderGenerator.cs

 
             if (combinedRequirements.requiresScreenPosition)
             {
-                var screenPosition = "ComputeScreenPos(mul(GetWorldToHClipMatrix(), mul(GetObjectToWorldMatrix(), v.vertex.xyz)), _ProjectionParams.x)";
+                var screenPosition = "ComputeScreenPos(mul(GetWorldToHClipMatrix(), mul(GetObjectToWorldMatrix(), v.vertex)), _ProjectionParams.x)";
                 vertexShader.AppendLine("float4 {0} = {1};", ShaderGeneratorNames.ScreenPosition, screenPosition);
                 if (graphModelRequirements.requiresScreenPosition)
                 {