Add ability to dynamically extend the layout inspector sidebar

Summary: This adds the ability to extend the layout inspector's sidebar via SidebarExtensions

Reviewed By: sjkirby

Differential Revision: D8677332

fbshipit-source-id: 1880d5d2185306290a278e8a48e965ad94b98cc0

src/fb-stubs/LayoutInspectorSidebarExtensions.js

@@ -0,0 +1,7 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+export default [];

src/ui/components/elements-inspector/sidebar.js

@@ -12,6 +12,7 @@ import ManagedDataInspector from '../data-inspector/ManagedDataInspector.js';
 import {Component} from 'react';
 import {Console} from '../console';
 import {GK} from 'sonar';
+import SidebarExtensions from '../../../fb-stubs/LayoutInspectorSidebarExtensions.js';
 
 const deepEqual = require('deep-equal');
 
@@ -109,7 +110,10 @@ export class InspectorSidebar extends Component<Props, State> {
       return null;
     }
 
-    const sections = [];
+    const sections = SidebarExtensions.map(ext =>
+      ext(this.props.client, element.id),
+    );
+
     for (const key in element.data) {
       sections.push(
         <InspectorSidebarSection