ProjectExplorer: Make project window state persistent

Task-number: QTCREATORBUG-24690
Change-Id: Ia261fc5a98681676e8d67e6d840f2f48073cdbb2
Reviewed-by: hjk <hjk@qt.io>

src/plugins/projectexplorer/projectwindow.h

@@ -64,6 +64,12 @@ public:
     void activateProjectPanel(Utils::Id panelId);
 
 private:
+    void hideEvent(QHideEvent *event) override;
+    void showEvent(QShowEvent *event) override;
+
+    void savePersistentSettings() const;
+    void loadPersistentSettings();
+
     const std::unique_ptr<ProjectWindowPrivate> d;
 };