Change specularAmbientOcclusion from boolean to enum (#2352)

The user can now choose amongst 3 specular AO methods:
- None, specAO is off
- Simple, specAO is inferred from roughness and diffuse AO
- Bent normals, specAO is computed accurately from cone intersections

The last method is more expensive but produces the best results.

This change also fixes a few issues:
- Rename materialRefraction() and materialRefractionType() for
  consistency
- Fixes user time in shaders

libs/gltfio/src/MaterialGenerator.cpp

@@ -242,7 +242,7 @@ Material* createMaterial(Engine* engine, const MaterialKey& config, const UvMap&
     MaterialBuilder builder = MaterialBuilder()
             .name(name)
             .flipUV(false)
-            .specularAmbientOcclusion(true)
+            .specularAmbientOcclusion(MaterialBuilder::SpecularAmbientOcclusion::SIMPLE)
             .material(shader.c_str())
             .doubleSided(config.doubleSided)
             .targetApi(filamat::targetApiFromBackend(engine->getBackend()));