feat(external_api): Add command for toggling localFlipX

modules/API/API.js

     pinParticipant,
     kickParticipant
 } from '../../react/features/base/participants';
+import { updateSettings } from '../../react/features/base/settings';
 import { isToggleCameraEnabled, toggleCamera } from '../../react/features/base/tracks';
 import { setPrivateMessageRecipient } from '../../react/features/chat/actions';
 import { openChat } from '../../react/features/chat/actions.web';
 
             APP.store.dispatch(toggleCamera());
         },
+        'toggle-camera-mirror': () => {
+            const state = APP.store.getState();
+            const { localFlipX: currentFlipX } = state['features/base/settings'];
+
+            APP.store.dispatch(updateSettings({ localFlipX: !currentFlipX }));
+        },
         'toggle-chat': () => {
             sendAnalytics(createApiEvent('chat.toggled'));
             APP.UI.toggleChat();

modules/API/external/external_api.js

     submitFeedback: 'submit-feedback',
     toggleAudio: 'toggle-audio',
     toggleCamera: 'toggle-camera',
+    toggleCameraMirror: 'toggle-camera-mirror',
     toggleChat: 'toggle-chat',
     toggleFilmStrip: 'toggle-film-strip',
     toggleRaiseHand: 'toggle-raise-hand',