Updated with fixes for `convertsystemimages.xsl`:
- Use `type-details/codename` if it exists, falling back to
`type-details/api-level`: this results in "Q" rather than "28" for
preview images
- Use `<xsl:text>` elements to control whitespace in the output.
This is extracted from https://github.com/NixOS/nixpkgs PR 58131.