Re-commit "Generalize scene description for automated testing (#9627)"

Contains a fix to the default sunlight parameters that broke the
renderdiff tests.

docs_src/build/duplicates.json

@@ -49,6 +49,9 @@
     "libs/fgviewer/README.md": {
         "dest": "dup/fgviewer.md"
     },
+    "libs/viewer/README.md": {
+        "dest": "dup/viewer.md"
+    },
     "ios/CocoaPods/README.md": {
         "dest": "release/cocoapods.md"
     },

docs_src/src_mdbook/src/SUMMARY.md

@@ -41,6 +41,7 @@
     - [gltfio](./dup/gltfio.md)
     - [iblprefilter](./dup/iblprefilter.md)
     - [matdbg](./dup/matdbg.md)
+    - [viewer](./dup/viewer.md)
     - [uberz](./dup/uberz.md)
   - [Tools](./notes/tools.md)
     - [beamsplitter](./dup/beamsplitter.md)