feat: provide usable UMD builds for all packages (#2141)

packages/netlify-cms-widget-text/src/index.js

@@ -1,2 +1,5 @@
-export TextControl from './TextControl';
-export TextPreview from './TextPreview';
+import controlComponent from './TextControl';
+import previewComponent from './TextPreview';
+
+export const NetlifyCmsWidgetText = { controlComponent, previewComponent };
+export { controlComponent, previewComponent };