feat(pbxproj): add build file in add_file

Author: kkharji

src/pbxproj/object/fs/mod.rs

@@ -239,9 +239,13 @@ impl PBXFSReference {
         let children_references = self.children_references.get_or_insert(Default::default());
 
         if !children_references.contains(&reference) {
-            children_references.insert(reference);
+            children_references.insert(reference.clone());
         };
 
+        let mut build_file = PBXBuildFile::default();
+        build_file.set_file_reference(reference.into());
+        let _reference = objects.push(file_reference.clone());
+
         Ok(file_reference)
     }
 }