A conflict that the resolution process encountered
@attr [Object] requirement the requirement that immediately led to the conflict
@attr [{String,Nil=>[Object]}] requirements the requirements that caused the conflict
@attr [Object, nil] existing the existing spec that was in conflict with
the {#possibility}
@attr [Object] possibility_set the set of specs that was unable to be
activated due to a conflict.
@attr [Object] locked_requirement the relevant locking requirement.
@attr [Array<Array