These functions will be used when it is necessary to determine the best size
of the control if one of its size components is fixed. Currently none of the
classes implements DoGetBestClient{Height,Width}() yet but wxListCtrl will do
it soon, see #13898.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71392 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775