Function perform_replacement 

pub fn perform_replacement(
    search_results: Vec<SearchResultWithReplacement>,
    background_processing_sender: UnboundedSender<BackgroundProcessingEvent>,
    cancelled: Arc<AtomicBool>,
    replacements_completed: Arc<AtomicUsize>,
    event_sender: UnboundedSender<Event>,
    validation_search_config: Option<FileSearcher>,
    file_content_provider: Arc<dyn FileContentProvider>,
) -> JoinHandle<()>