Type improvements

Summary: some type simplifications, that makes it easier to reuse data sources and helps type inference

Reviewed By: passy

Differential Revision: D28413380

fbshipit-source-id: 261a8b981bf18a00edc3075926bd668322e1c37d

desktop/flipper-plugin/src/data-source/index.tsx

@@ -7,7 +7,7 @@
  * @format
  */
 
-export {DataSource, ExtractKeyType} from './DataSource';
+export {DataSource, createDataSource, DataSourceOptions} from './DataSource';
 export {
   DataSourceRendererVirtual,
   DataSourceVirtualizer,