api: add private message flag to outgoingMessage

modules/API/API.js

      * Notify external application (if API is enabled) that message was sent.
      *
      * @param {string} message - Message body.
+     * @param {boolean} privateMessage - True if the message was a private message.
      * @returns {void}
      */
-    notifySendingChatMessage(message: string) {
+    notifySendingChatMessage(message: string, privateMessage: boolean) {
         this._sendEvent({
             name: 'outgoing-message',
-            message
+            message,
+            privateMessage
         });
     }
 

react/features/chat/middleware.js

             } else {
                 // Sending the message if privacy notice doesn't need to be shown.
 
+                const { privateMessageRecipient } = state['features/chat'];
+
                 if (typeof APP !== 'undefined') {
-                    APP.API.notifySendingChatMessage(action.message);
+                    APP.API.notifySendingChatMessage(action.message, Boolean(privateMessageRecipient));
                 }
 
-                const { privateMessageRecipient } = state['features/chat'];
-
                 if (privateMessageRecipient) {
                     conference.sendPrivateTextMessage(privateMessageRecipient.id, action.message);
                     _persistSentPrivateMessage(store, privateMessageRecipient.id, action.message);