What problem does your feature solve?

The lib parameter on contracttype/contracterror/contractevent macros is a hidden, unused feature. It's undocumented and never turned out to be something that was usable. On mainnet there are zero contracts using it and there are no situations where the feature would be recommended for use.

If someone discovers it and starts using it, they probably shouldn't.

What would you like to see?

Deprecate it, and remove it once it has been deprecated for a little while.

What alternatives are there?

Remove it now, or leave it forever.