When a constraint fails, display _which_ constraint failed to make it easier to debug

[noahnu]

If you have a project with 10s of constraints and you see a failure, it's difficult to tell which constraint was the one causing the failure. You have to read through all the constraints again (and try to remember prolog which you only write in for yarn constraints 😄 ). Having some sort of label/identifier would be helpful.

I know there are plans to rewrite constraints in typescript, in that case, I'd like to extend the feature request to that new system.