Split flipper-plugin package

Summary:
flipper-server-companion depends on flipper-plugin. flipper-plugin includes dependencies that run only in a browser. Splitting flipper-plugin into core and browser packages helps to avoid including browser-only dependencies into flipper-server bundle.
As a result, bundle size could be cut in half. Subsequently, RSS usage drops as there is twice as less code to process for V8.

Note: it currently breaks external flipper-data-source package. It will be restored in subsequent diffs

Reviewed By: lblasa

Differential Revision: D38658285

fbshipit-source-id: 751b11fa9f3a2d938ce166687b8310ba8b059dee

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

@@ -9,11 +9,11 @@
 
 export {
   DataSource,
-  DataSourceView,
+  _DataSourceView,
   createDataSource,
-  DataSourceOptions,
-  DataSourceOptionKey,
-} from './DataSource';
+  _DataSourceOptions,
+  _DataSourceOptionKey, // eslint-disable-next-line node/no-extraneous-import
+} from 'flipper-plugin-core';
 export {
   DataSourceRendererVirtual,
   DataSourceVirtualizer,