Revert "Revert "gltfio: enable specular AO to "fix" #1870""

This reverts commit f9230856af.

libs/gltfio/materials/ubershader.mat.in

@@ -6,6 +6,7 @@ material {
     depthWrite : true,
     doubleSided : ${DOUBLESIDED},
     flipUV : false,
+    specularAmbientOcclusion: true,
     parameters : [
 
         { type : float3, name : specularFactor },

libs/gltfio/src/MaterialGenerator.cpp

@@ -202,6 +202,7 @@ Material* createMaterial(Engine* engine, const MaterialKey& config, const UvMap&
     MaterialBuilder builder = MaterialBuilder()
             .name(name)
             .flipUV(false)
+            .specularAmbientOcclusion(true)
             .material(shader.c_str())
             .doubleSided(config.doubleSided)
             .targetApi(filamat::targetApiFromBackend(engine->getBackend()));