Override wxWindow::MSWGetCreateWindowCoords() in wxTopLevelWindow.

Override wxWindow::MSWGetCreateWindowCoords() in wxTopLevelWindow.

The old code was messy because it handled both top level and child windows at
wxWindow level when they need quite different treatment. This resulted in
several errors: first, wxWindow versions of WidthDefault and HeightDefault
were used to determine the initial size even of top level windows which was
clearly wrong as it created tiny windows (20*20). Second, CW_USEDEFAULT could
be used for child window for which this shouldn't be done.

Fix this by making MSWGetCreateWindowCoords() virtual and overriding it in
wxTopLevelWindow. This makes the code much simpler and more obviously correct.

Also make MSWGetCreateWindowCoords() void, as nobody was using its return
value anyhow (and the old version also had a bug in it and wrongly returned
true when default size was passed to it).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64101 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775