Fail fast if the input problem is not "disjoint"

if input has the same task in 2 taskLists, fail fast (=> not disjoint)

https://github.com/kiegroup/optaplanner/pull/1494#issuecomment-893556221

Reconsider this requirement. Decide if it's user-friendly, technically doable without a performance impact.

Maybe this is already implemented. The inverse/index shadow variable supplies and listeners probably already fail on this. TODO confirm.