Add wxTreeCtrl::{Clear,Set}FocusedItem().

Allow changing just the currently focused (not selected) item and also
removing the focus completely.

Closes #11599.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64196 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/treectlg.h

@@ -122,6 +122,9 @@ public:
     virtual size_t GetSelections(wxArrayTreeItemIds&) const;
     virtual wxTreeItemId GetFocusedItem() const { return m_current; }
 
+    virtual void ClearFocusedItem();
+    virtual void SetFocusedItem(const wxTreeItemId& item);
+
     virtual wxTreeItemId GetItemParent(const wxTreeItemId& item) const;
     virtual wxTreeItemId GetFirstChild(const wxTreeItemId& item,
                                        wxTreeItemIdValue& cookie) const;