Codechange: make WindowClass a scoped enum

src/textfile_gui.cpp

@@ -78,7 +78,7 @@ static constexpr std::initializer_list<NWidgetPart> _nested_textfile_widgets = {
 /** Window definition for the textfile window */
 static WindowDesc _textfile_desc(
 	WindowPosition::Center, "textfile", 630, 460,
-	WC_TEXTFILE, WC_NONE,
+	WindowClass::Textfile, WindowClass::None,
 	{},
 	_nested_textfile_widgets
 );