Use the task dialog instead of the legacy message box for wxMessageDialog
implementation under wxMSW on recent (Vista and later) Windows versions.
As part of this change, remove wxMessageDialogWithCustomLabels and integrate
its functionality in wxMessageDialogBase itself as it's now used by all
platforms.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65348 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
