Allow wxAuiDeserializer::CreatePaneWindow() to modify pane info

wxAuiPaneInfo fields such as "caption" or "icon" wouldn't normally be
serialized and so CreatePaneWindow() should be allowed to fill them in.

include/wx/aui/serializer.h

@@ -89,7 +89,11 @@ public:
     // layout and allows to create windows on the fly.
     //
     // If this function returns nullptr, the pane is not added to the manager.
-    virtual wxWindow* CreatePaneWindow(const wxAuiPaneInfo& WXUNUSED(pane))
+    //
+    // Note that the pane may (and usually will, if a window is created) be
+    // modified, to set fields such as caption or icon that wouldn't normally
+    // be serialized.
+    virtual wxWindow* CreatePaneWindow(wxAuiPaneInfo& WXUNUSED(pane))
     {
         return nullptr;
     }

interface/wx/aui/serializer.h

@@ -175,8 +175,13 @@ public:
 
         If this function returns @NULL, as it does by default, the pane is not
         added to the manager.
+
+        If the function does create a new window, it should typically modify @a
+        pane parameter to fill in the fields such as `caption` or `icon` that
+        wouldn't normally be serialized and so wouldn't be restored by
+        LoadPanes().
      */
-    virtual wxWindow* CreatePaneWindow(const wxAuiPaneInfo& pane);
+    virtual wxWindow* CreatePaneWindow(wxAuiPaneInfo& pane);
 
     /**
         Load information about all the docks previously saved with SaveDock().

samples/aui/auidemo.cpp

@@ -1724,7 +1724,7 @@ public:
         return panes;
     }
 
-    virtual wxWindow* CreatePaneWindow(const wxAuiPaneInfo& pane) override
+    virtual wxWindow* CreatePaneWindow(wxAuiPaneInfo& pane) override
     {
         wxLogWarning("Unknown pane \"%s\"", pane.name);
         return nullptr;