Codechange: Use std::initializer_list for NWidgetPart data. (#14749)

Avoids using C/C++ arrays.

src/main_gui.cpp

@@ -187,7 +187,7 @@ void FixTitleGameZoom(int zoom_adjust)
 	UpdateViewportSizeZoom(vp);
 }
 
-static constexpr NWidgetPart _nested_main_window_widgets[] = {
+static constexpr std::initializer_list<NWidgetPart> _nested_main_window_widgets = {
 	NWidget(NWID_VIEWPORT, INVALID_COLOUR, WID_M_VIEWPORT), SetResize(1, 1),
 };