Aqua Swatch is a reference application, it allows you the developer to see what the actual colors, icons, font settings and vibrancy look like, as opposed to Apple’s documentation which just gives you the names. You can also run this macOS 10.13 or newer to see how the icons are different across different OS versions.
To use the icons with Xojo, you’ll need either a 3rd Party collection (such as my own Ohanaware App Kit, the MBS plugin) or a bunch of declares. As Ian’s code is close, with a little more work, his code should be able to allow you to use these icons within your application also.
Typically you don’t rasterize system icons unless you want the icons to be consist across all supported OS versions or the icon you want isn’t available in a supported OS version. i.e. App Wrapper not only features a tool for rasterizing SF Symbols (and including them within your application), but also includes a whole bunch within as App Wrapper supports 10.13 and newer.