improve mixpanel usage statistics (#2238)

Other changes:
- Always display first start dialog if privacy options are unset (e.g. if the user closed GPT4All without selecting them)
- LocalDocs scanQueue is now always deferred
- Fix a potential crash in magic_match
- LocalDocs indexing is now started after the first start dialog is dismissed so usage stats are included

Signed-off-by: Jared Van Bortel <jared@nomic.ai>

gpt4all-chat/chat.h

@@ -143,7 +143,7 @@ private Q_SLOTS:
     void handleResponseChanged(const QString &response);
     void handleModelLoadingPercentageChanged(float);
     void promptProcessing();
-    void responseStopped();
+    void responseStopped(qint64 promptResponseMs);
     void generatedNameChanged(const QString &name);
     void handleRecalculating();
     void handleModelLoadingError(const QString &error);
@@ -175,6 +175,7 @@ private:
     bool m_shouldDeleteLater = false;
     float m_modelLoadingPercentage = 0.0f;
     LocalDocsCollectionsModel *m_collectionModel;
+    bool m_firstResponse = true;
 };
 
 #endif // CHAT_H