Fix upload progress not communicating processing phase in web UI (#19530)

app/javascript/mastodon/features/compose/containers/upload_progress_container.js

@@ -4,6 +4,7 @@ import UploadProgress from '../components/upload_progress';
 const mapStateToProps = state => ({
   active: state.getIn(['compose', 'is_uploading']),
   progress: state.getIn(['compose', 'progress']),
+  isProcessing: state.getIn(['compose', 'is_processing']),
 });
 
 export default connect(mapStateToProps)(UploadProgress);