feat: export downloadBlob function

In preparation for being able to download the Scratch program in
experience-cs from outside of scratch-gui.

Co-authored-by: Chris Lowis <chris.lowis@gofreerange.com>
Co-authored-by: James Mead <james.mead@gofreerange.com>

Author: 3 people

packages/scratch-gui/src/index.ts

@@ -5,6 +5,7 @@ export {default} from './containers/gui.jsx';
 export {default as GUIComponent} from './components/gui/gui.jsx';
 export {default as AppStateHOC} from './lib/app-state-hoc.jsx';
 export {manualUpdateProject, remixProject} from './reducers/project-state.js';
+export {default as downloadBlob} from './lib/download-blob.js';
 export {setAppElement} from 'react-modal';
 
 export {legacyConfig};