[Non-urgent] Adopt new Fabric distribution conventions

[asiekierka]

The old ones will continue to work, but the new ones are so much better.

1. Instead of fiddling with maven-metadata, there is now a standard for querying information about these Fabric components - the fabric-meta API.
2. Instead of using Yarn versions, Intermediary versions can now be used - with no detriment to the end user, but they always have a 1<->1 relation to Minecraft versions, so it's very easy to derive which version should be used - unlike Yarn, which makes it confusing sometimes.