Add wxWindow::BeginRepositioningChildren() and EndRepositioningChildren().

This is just a refactoring of wxMSW code to make it possible to use deferred
window positioning from other places in subsequent commits.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74066 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/window.h

@@ -67,6 +67,9 @@ public:
     virtual void Raise();
     virtual void Lower();
 
+    virtual bool BeginRepositioningChildren();
+    virtual void EndRepositioningChildren();
+
     virtual bool Show(bool show = true);
     virtual bool ShowWithEffect(wxShowEffect effect,
                                 unsigned timeout = 0)