Add a PBR shader code coverage test

tests/validation/config.json

@@ -677,6 +677,11 @@
             "referenceImage": "pbr_refraction.png"
         },
         {
+            "title": "PBR shader code coverage",
+            "playgroundId": "#QI7TL3#3",
+            "referenceImage": "pbr_codecoverage.png"
+        }
+        {
             "title": "Texture cache",
             "playgroundId": "#20OAV9#237",
             "referenceImage": "texture cache.png"

tests/validation/validation.js

@@ -33,6 +33,7 @@ function compare(renderData, referenceCanvas, threshold, errorRatio) {
         referenceData.data[index] = 255;
         referenceData.data[index + 1] *= 0.5;
         referenceData.data[index + 2] *= 0.5;
+        referenceData.data[index + 3] = 255;
         differencesCount++;
     }