message: [core/AppBuilder] collect list of registered feature flags
diff: @@ -19,6 +19,7 @@ import { Route, Switch, Redirect } from 'react-router-dom';
  import { AppContextProvider } from './AppContext';
  import { App } from './types';
  import BackstagePlugin from '../plugin/Plugin';
  +import { FeatureFlagName } from '../plugin/Plugin/types';
  import {
  IconComponent,
  SystemIcons,
  @@ -62,6 +63,7 @@ export default class AppBuilder {
  const app = new AppImpl(this.systemIcons);
  const routes = new Array<JSX.Element>();
  + const registeredFeatureFlags = new Array<{ name: FeatureFlagName }>();
  for (const plugin of this.plugins.values()) {
  for (const output of plugin.output()) {
  @@ -87,6 +89,10 @@ export default class AppBuilder {
  );
  break;
  }
  + case 'feature-flag': {
  + registeredFeatureFlags.push({ name: output.name });
  + break;
  + }
  default:
  break;
  }
  