fixing plugin imports

Summary:
Plugins need to be self-contained. The can not require any dependency from Flipper's main app. This was a soft requirement before, but with the new version of metro, we now make this a hard requirement.

This speeds up plugin compile times, because only the files in the plugin's folder are watched and not all of Flipper's files. Moreover, this ensures "plugins" are real plugins and can be added and removed and are not mixed with the apps core.

Reviewed By: passy

Differential Revision: D9940735

fbshipit-source-id: 47e120429fc3c4c985731478ffa35c3359ff78f9

src/plugins/layout/index.js

@@ -25,10 +25,10 @@ import {
   VerticalRule,
   Popover,
   ToggleButton,
+  SidebarExtensions,
 } from 'flipper';
 
 import type {TrackType} from '../../fb-stubs/Logger.js';
-import SidebarExtensions from '../../fb-stubs/LayoutInspectorSidebarExtensions.js';
 
 import debounce from 'lodash.debounce';