Rename wxGenericDirCtrl::ExpandDir() to PopulateNode().

This function doesn't really expand anything (unlike CollapseDir()) so give it
a better name while keeping the old one too for compatibility.

See #12735.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66315 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/dirctrlg.h

@@ -189,6 +189,8 @@ protected:
     bool ExtractWildcard(const wxString& filterStr, int n, wxString& filter, wxString& description);
 
 private:
+    void PopulateNode(wxTreeItemId node);
+
     bool            m_showHidden;
     wxTreeItemId    m_rootId;
     wxString        m_defaultPath; // Starting path