Codechange: Replace mishmash of types for widget index with WidgetID.

Indices were stored as int, but often passed around as uint/uint8_t and casts.

Now they should all use WidgetID.

src/screenshot_gui.cpp

@@ -27,7 +27,7 @@ struct ScreenshotWindow : Window {
 		this->DrawWidgets();
 	}
 
-	void OnClick([[maybe_unused]] Point pt, int widget, [[maybe_unused]] int click_count) override
+	void OnClick([[maybe_unused]] Point pt, WidgetID widget, [[maybe_unused]] int click_count) override
 	{
 		ScreenshotType st;
 		switch (widget) {