Add support for wxICON_AUTH_NEEDED to wxMessageDialog.

Allow showing the standard "Authentication needed" dialog in the message boxes
under MSW.

Closes #15121.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73877 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/dialogs/dialogs.cpp

@@ -3005,7 +3005,8 @@ bool TestMessageBoxDialog::Create()
         "&Information icon",
         "&Question icon",
         "&Warning icon",
-        "&Error icon"
+        "&Error icon",
+        "A&uth needed icon"
     };
 
    wxCOMPILE_TIME_ASSERT( WXSIZEOF(icons) == MsgDlgIcon_Max, IconMismatch );
@@ -3106,6 +3107,10 @@ long TestMessageBoxDialog::GetStyle()
         case MsgDlgIcon_Error:
             style |= wxICON_ERROR;
             break;
+
+        case MsgDlgIcon_AuthNeeded:
+            style |= wxICON_AUTH_NEEDED;
+            break;
     }
 
     if ( m_chkCentre->IsChecked() )