this is a relatively simple recasting of the existing update script,
using the "object addition" feature of 'jq' to incrementally update
the eclipses.json document with the URL components and their hashes.
it does end up defining the same update script for every eclipse
packaging, but in local testing, maintainers/scripts/update.nix seems
smart enough to realize it should only run that script once.
this isn't complete enough to use as a formal updateScript yet, but
it's definitely an improvement over the current purely-manual process.
Co-authored-by: Robert Helgesson <robert@rycee.net>
