Provide a task-dialog based wxMSW wxMessageDialog implementation.

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

interface/wx/msgdlg.h

@@ -47,6 +47,8 @@
     @style{wxICON_QUESTION}
         Displays a question mark symbol. This icon is automatically used
         with @c wxYES_NO so it's usually unnecessary to specify it explicitly.
+        This style is not supported for MSW task dialogs, as question icons do
+        not follow the guidelines. No icon will be displayed in this case.
     @style{wxICON_INFORMATION}
         Displays an information symbol. This icon is used by default if
         @c wxYES_NO is not given so it is usually unnecessary to specify it
@@ -56,7 +58,9 @@
         just its parent (currently implemented only under MSW and GTK).
     @style{wxCENTRE}
         Centre the message box on its parent or on the screen if parent is not
-        specified (currently only implemented under MSW).
+        specified.
+        Setting this style under MSW makes no differences as the dialog is
+        always centered on the parent.
     @endStyleTable
 
     @library{wxcore}