Change wxMSW wxTreeCtrl::DoFreeze() to not hide the tree any more.

Hiding the tree when it's frozen, as done in r72665, results in its own
problems, e.g. loss of focus. So don't do this but resize the control to a
very small size when freezing it and restore it to its old size afterwards.

Closes #15166.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74072 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/treectrl/treetest.h

@@ -242,6 +242,7 @@ public:
     void OnSortRev(wxCommandEvent& WXUNUSED(event)) { DoSort(true); }
 
     void OnAddItem(wxCommandEvent& event);
+    void OnAddManyItems(wxCommandEvent& event);
     void OnInsertItem(wxCommandEvent& event);
 
     void OnIncIndent(wxCommandEvent& event);
@@ -350,6 +351,7 @@ enum
     TreeTest_EnsureVisible,
     TreeTest_SetFocus,
     TreeTest_AddItem,
+    TreeTest_AddManyItems,
     TreeTest_InsertItem,
     TreeTest_IncIndent,
     TreeTest_DecIndent,