Accessibility Inspector open-sourcing move and documentation

Summary: Replaces AXElementsInpector with normal inspector implementation, removes gating from external builds. Adds documentation to https://fbflipper.com/docs/layout-plugin.html.

Reviewed By: passy

Differential Revision: D9438713

fbshipit-source-id: 18616c6cbab339bf474d116cac128e1d4a5fc2be

src/fb-stubs/AXLayoutExtender.js

@@ -1,34 +0,0 @@
-/**
- * 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
- */
-
-import {Component} from 'react';
-import type {
-  Element,
-  ElementID,
-  ElementSearchResultSet,
-  ContextMenuExtension,
-} from 'sonar';
-
-export class AXElementsInspector extends Component<{
-  onElementExpanded: (key: ElementID, deep: boolean) => void,
-  onElementSelected: (key: ElementID) => void,
-  onElementHovered: ?(key: ?ElementID) => void,
-  onValueChanged: ?(path: Array<string>, val: any) => void,
-  selected: ?ElementID,
-  focused: ?ElementID,
-  searchResults?: ?ElementSearchResultSet,
-  root: ?ElementID,
-  elements: {[key: ElementID]: Element},
-  useAppSidebar?: boolean,
-  contextMenuExtensions: Array<ContextMenuExtension>,
-}> {
-  render() {
-    return null;
-  }
-}
-
-export const AXToggleButtonEnabled: boolean = false;