Allow disabling saving wxFileConfig data when it is destroyed

This can be useful to avoid saving the changes performed by the user if
this turns out to be undesirable, for whatever reason.

Closes https://github.com/wxWidgets/wxWidgets/pull/1451

Closes #13788.

include/wx/fileconf.h

@@ -182,6 +182,9 @@ public:
   virtual bool Save(wxOutputStream& os, const wxMBConv& conv = wxConvAuto());
 #endif // wxUSE_STREAMS
 
+  void EnableAutoSave() { m_autosave = true; }
+  void DisableAutoSave() { m_autosave = false; }
+
 public:
   // functions to work with this list
   wxFileConfigLineList *LineListAppend(const wxString& str);
@@ -250,6 +253,7 @@ private:
 #endif // __UNIX__
 
   bool m_isDirty;                       // if true, we have unsaved changes
+  bool m_autosave;                      // if true, save changes on destruction
 
   wxDECLARE_NO_COPY_CLASS(wxFileConfig);
   wxDECLARE_ABSTRACT_CLASS(wxFileConfig);